Can you crossfire two Radeon HD 6950's?
When i built my Pc, i bought one, but I need for graphics processing power when i stream live gameplay. I don't want to buy a better one because that'd be wasting my current one cuz GPUs seem hard to sell. Would it run well if i Xfired two of them? Do i need to buy the exact same card? is 750W enough?
I currently have 2 6950's both MSI Twin Frozr III PE/OC's Crossfired in my Sabertooth x79. I am having issues with it. I used the AMD wipe utility to uninstall the driver. I then hooked in the second card (no onboard graphics) booted up and installed driver.
Rebooted the computer again and made sure Crossfire was enabled. I used Passmark benchtests and looked at the Razer game booster and both state no increase in performance and only 2 G/B of Video RAM, each card is 2GB.
I am currently downloading Crysis 3 to see if it can run it at above medium specs.
Also, I run Eyefinity in case that would matter.
I need some guidance as how to determine whether or not the crossfire works.
The amount of ram is correct. VRAM does not add up in CF or SLI configurations. CF'd 6950s should give you close to a 6990 performance and should be able to run crysis 3 on very high at 1080p while sustaining ~50fps. at 3x1080p? medium? have you tried comparing 3dmark scores with other 6950 cf'd setups?
As au_equus stated VRAM is not additive, you're still limited by the VRAM bandwidth of the primary card (2GB in this case). What 750W power supply do you have? a quality one will suffice but a cheap PSU may not. I cant speak for what FPS you could get on Crysis 3 but you may be able to unlock (depending when you bought the card(s)) the 6970 shaders giving you better than a 6990 in performance (in CF).
Does eyefinity matter? well of course, your pumping out 3 times the pixel rate, thus you need ~ 3 times the graphics power to get the same FPS as a single monitor set up (a simplified assumption). I run Eyefinity @ 6048x1080 with essentially 3 x 6970's and I don't plan on being able to run Crysis 3 on High (I like to maintain around 55-60FPS).
So in full, yes crossfire works, you can expect around a 80% increase in FPS (that's conservative, and only for the first CF card, the second and third see diminishing returns) but your eyefinity setup will take allot of GPU power, Medium settings may be the best you will get with a decent frame rate.
Here is an article comparing many cards on Crysis 3 : http://www.guru3d.com/articles_pages/crysis_3_graphics_performance_review_benchmark,1.html
as you can see even 1 6950 on only a single monitor gives a less than playable framerate although it is on High settings. Read from that what you can. Hope that helps.