Having been a long-time Nvidia/SLI user, this is my first venture into AMD cards. I have a HD 6850 on a 1155 motherboard that has 2 PCI-E x16 slots. 1 runs at x16 and the other at x4. Up till now I have assumed the x4 slot was worthless in Crossfire. But having read some reviews, it seems that while there will be some loss if the 2nd card is in a x4 slot, there is still quite a bit of improvement over a single card. So... I decided to try Crossfire with a 2nd card.
But I have a few questions I hope someone can answer. Newegg has a Sapphire HD 6850 Toxic on sale now for the same price as the std version. Will the two cards works at the slowest clock speeds of the two cards, or will the Toxic still run at its rated speed?
And are there any issues mixing cards from different manufacturers?
And last, if I were to go to an HD 6790 instead for the 2nd card, would the HD 6850 'slow down' to match the HD 6790?
Sorry... just noticed most of my questions were answered in the Crossfire/SLI FAQs. My bad...
But feel free to add anything you feel pertinent, thanks
The cards will run at the speed they are set at. It is best to get two cards that run at the same speed, but if not try to overclock the slowest card to match the overclocked card.
Ahh, I see. Then what happens with the HD 6790 in the second slot? (It's even less expensive) The 6790 actually has faster clocks than the 6850. Will the 6850 slow down the lesser 6790? Sorry to be so dense.
The 6850 is the faster card since it has more shaders and rops enabled. Even though it is clocked lower, it is doing more work per clock than the 6790 while using less power. Anyway, yes crossfire is flexible in that you can crossfire two different cards like the 6790 and 6850, but when you do that and you are using Alternate Frame Rendering one frame is being drawn faster than the next frame waiting on the slower card. That can give you the effect of microstuter.
Of course this all depends on the game since crossfire does have a few different modes of rendering a scene. In modes where both cards are rendering the scene you could just be held up finishing the scene by the slower card (so it would be like having two 6790s) or if the driver is in tiling mode and the game offloads more tiles to the faster card then it would be a little better than just two 6790s. As for the microstutter that may not even bother you. It bothers some people more than others.
I guess I forgot to mention that I already had a 6850 in slot 1. I was just wondering if I should buy the less expensive 6790 or go for the slightly more expensive 6850 (being as how the 2nd card was going in the lowly x4 slot). But thank you. I considered your advice and opted for a 2nd 6850. I received some very good advice and learned something about Crossfire along the way. Thanks again...