650M SLI vs 650M and 750M SLI vs 765M: SLI performance investigation

The SLI equipped laptops were not that interesting in my eyes until not long ago, about half a year ago. Laptops with GPUs in SLI (or CFx) belonged to the higher price range (~2000$ and up) and therefore were not very accessible and probably not very interesting to the vast majority of the buyers.

But since Lenovo started with their Y500/Y400 ultrabay enabled line, things have change. The Y500 especially, sports an 1080p screen, good enough build quality and a GT 650M SLI and later on a GT 750M, burst out of the performance/price curve compared to the available gaming laptops then. I was skeptic about this SLI solution, but it appear to make the Y500 an excellent performer for a low price, relatively. For 900$-1000$ you could get the Y500 with 650M SLI, I5/I7 CPU, 6GB/8GB DDR3, 1080p screen, 1TB HDD (sometimes with a 16GB mSata drive) and a Windows OS, including shipping and depends on your location – also tax. The 650M actually performed very well in games according to benchmarks and users, sometimes getting twice or almost twice the performance compared to a single GT 650M, scoring even higher than the GTX 670MX which equipped much more expensive and usually heavy gaming laptops.

The Y510p adds to this with a matte screen, 24GB mSSD (not an mSata, but M.2 port), Haswell CPU and maybe some other things beyond raw specs that should be tested in a review.

In this post, I want to cover the performance difference of the 650M SLI and deduce also the 750M SLI performance from that.

ModelCore, shaders (vertex / geometry / pixel)MemoryCore speed
GT 650MKepler (GK107), 384 unified : 32 : 16, 28nm processGDDR5@1GHZ735MHZ - 800MHZ/850MHZ (boost)
GT 750MKepler (GK107), 384 unified : 32 : 16, 28nm processGDDR5@1.25GHZ940MHZ - 970MHZ (boost)
GTX 765MKepler (GK106), 768 unified : 64 : 16, 28nm processGDDR5@1GHZ850MHZ

Not that we really need this table, but just to make things clear – the 650M and 750M are practically the same chip as far as performance comparisons are required. The 750M is a 650M with higher clocks and some improvements (GPU Boost 2.0). The performance of the 750M should be around 15%-25% higher, depends on the specific clocks of the 650M, as they are differ.

We also see that the GTX 765M has twice the CUDA cores the 750M has, but the 750M has higher memory bandwidth (!) although being a much lower end card. Two 650Ms or 750M also have double the ROPs count effectively. Note, however, that not everything doubles up with SLI – the memory bandwidth is a complicated issue and in many cases you don’t get double the bandwidth. In SLI, the same data is fully copied to both GPUs, at least in the classic solution. But in many cases the SLI can have some advantage in memory bandwidth due to the way SLI works and the fact that for each frame to be rendered, the single 765M has still the same memory bandwidth which might limit the GPU and prevent it from fully utilize all its CUDA cores to their fullest potential. Another example is Anti-Aliasing – you can get a higher AA performance with SLI which is very reasonable.

 

We’ll now see some scores of the Y500 with 650M SLI vs single 650M:

GameSettingsGT 650MGT 650M SLIGTX 765M
Far Cry 31920x1080, Ultra high, 4xMSAA8-915-1614-15
Assassin´s Creed III1920x1080, very high AA AF1522-2323
Hitman: Absolution1920x1080 Ultra Preset 16xAF 4xAA9-1019-2014-15
Call of Duty: Black Ops 21920x1080 very high onAA 4xAF285550
Need for Speed: Most Wanted 1920x1080 high/on, AF AA17-1819-2036
Dishonored, high, FOV: 75 FXAA1920x1080 Very High, DX11 8xAF Very High FXAA52-5595-9680
Borderlands 21920x1080, high/on 8xAF, FXAA366047-50

I also included the GTX 765M results from NBC, but note that they are unreliable for determining the 765M potential, because NBC used a laptop that has a throttling problem. However, most of the results seems to be OK, based on the differences between the 765M, 760M and 770M.

The following table show the % difference of 650M vs 650M SLI, 650M SLI vs 765M and also guesstimating the 750M SLI vs GTX 765M difference – the results are certainly not accurate due to, as I mentioned above, throttling in NBC tests systems.

GameSettings650M vs 650M SLI difference (%)650M SLI vs 765M difference (%)750M SLI vs 765M difference guesstimation (%)
Far Cry 31920x1080, Ultra high, 4xMSAA+75%-80%~+0%-5%+20%-35%
Assassin´s Creed III1920x1080, very high AA AF~ +50%~0%+15%-35%
Hitman: Absolution1920x1080 Ultra Preset 16xAF 4xAA~+100%~+33%+50%-65%
Call of Duty: Black Ops 21920x1080 very high onAA 4xAF~+100%~+10%+10%-15%
Need for Speed: Most Wanted 1920x1080 high/on, AF AA~+10%~-45%-30%-40%
Dishonored, high, FOV: 75 FXAA1920x1080 Very High, DX11 8xAF Very High FXAA~+75%~+20%35%-50%
Borderlands 21920x1080, high/on 8xAF, FXAA~+66%~+20%35%-50%

The results are based on the NBC benchmarks (650M SLI, 765M). The 750M SLI vs 765M guesstimation is a simple calculation of the 650M vs 750M difference multiplied in the known 650M SLI vs 765M difference. This is a simple calculation but not necessarily correct more benchmarks are needed, plus the fact that some games’ are more sensitive to memory bandwidth and some to CPU and so on.

So, what do we see? That the 650M SLI has, averagely, an advantage over the GTX 765M. Sometimes, like in NFS, the SLI doesn’t really offer any significant advantage, but these are specific cases. In some cases, the 650M SLI has a very nice advantage of 20%-30% over the GTX 765M. That’s interesting. The GT 750M SLI should have even greater performance advantage.

 

Saying that and being safe, the SLI performance should really be great and we’ve seen with the 650M SLI. There is more support to this insight by looking at the Kepler desktop parts. For example, two GTX 650 Ti vs GTX 680. The GTX 650 Ti is practically an overclocked GTX 765M with core@~1000MHZ and memory@1500MHZ. The GTX 680 has double the core count, but about the same core clocks and memory clocks. Result? see for yourself – the SLI in most performs at least as good and in many cases outperforms the GTX 680 by a significant difference, including in makor titles like BF3, CoD: BO 2, BL2 and more.

The GTX 765M can be easily overclocked though and it should also be more energy efficient than the 650M/750M set. However, to see these advantages, we have to see some more laptops that make use of it.

 

SLI Problems/Bugs

The main problem with SLI is that is more prone to the micro-stuttering effect. In the case of Nvidia SLI, micro-stuttering sometimes exists, but it gets better with better drivers + you can use SLI adaptive VSync to improve things. Overall, I don’t think it should be a deal breaker. Many people report that they even haven’t seen micro-stuttering problems with their SLI solutions.

 

Conclusion

Currently, the GTX 765M and GT 650M/750M solutions are positioned at around the same price of 1000$-1100$ – check. I’d say that you should decide which laptop you prefer overall, keeping in mind that the 650M SLI and GTX 765M perform on about the same level. The 765M should have a battery performance advantage and also should have less problems with micro-stuttering and drivers, but the SLI solutions start to be a really good option and if you prefer the laptop in question overall, I’d say go for it.

  • Jimmy

    Just a quick note, when you mention the term “NBC,” I seriously thought you meant the National Broadcasting Company in U.S., and it made sense to me that a News company will not have the right resources aka specs to test out anything.

    • ((-:

      I guessed as much, but I thought it could be more funny than harmful, all these National things