Should you mismatch your GPUs? NO.

I am posting this as a general information post. Some people think that if they buy a faster GPU for their system they can just leave their old one in too and it will take some of the load. This is wrong.

Please see these numbers:


GTX 780 and GTX 780

No SLI
- One Monitor Plugged into second card. -> Average FPS: 51.0 Score 1285
- Two Monitors Plugged into second card. -> Average FPS: 47.6 Score 1199
- Three Monitors plugged into same card. -> Average FPS: 51.1 Score 1287

With SLI
(With Span with surround)
- One Monitor Plugged into second card. -> Average FPS: 50.8 Score 1280
- Two Monitors Plugged into second card. -> Average FPS: 50.2 Score 1264
- Three Monitors plugged into same card. -> For some reason it would not let me because Windows kept getting screwed up with the "expand desktop to this monitor" function.

(No Span with Surround)
- Three Monitors plugged into same card. -> Average FPS: 80.2 Score 2020
- You have to have all monitors on same card for 3D Optimized.



GTX 780 and GTS 450

No SLI (Main Display set to GTX 780
- One Monitor Plugged into second card. -> Average FPS: 45.1 Score 1137
- Two Monitors Plugged into second card. -> Average FPS: 45.1 Score 1135
- Three Monitors plugged into same card. -> Average FPS: 51.4 Score 1296

No SLI (Main Display set to GTS 450
- One Monitor Plugged into second card. -> Average FPS: 8.2 Score 207
- Two Monitors Plugged into second card. -> Average FPS: 7.6 Score 191
- Card only had 2 DVIs

I could not SLI the GTX 780 with the GTS 450. I tried but no go just as I figured (Nvidia says you can't do this).

If you look at these numbers you will note that the GPU the system decides to use for all of its processing is the one the Primary Monitor is on. If you have your primary monitor on your slower GPU then your results will be really slow because it will not use your faster GPU at all.

It is better to put all of your monitors in your fastest GPU regardless of the case even with SLI and without. It is also better to not use surround SLI. My guess is with surround SLI that you're making a really big virtual monitor and that is why it is slower.



Summary:

Your system will only use one GPU at a time unless you have SLI or Crossfire and in order to do that you must match GPUS. I hope this helps you and others.