I have a Core i5 750( Stock it clocks at 2.66ghz but I am planning on OC it to around 3.2ghz once I get an aftermarket heatsink.) and a XFX 4890. I am thinking about adding another 4890 as soon as they drop into the $150 dollar range. Anyways will my cpu bottleneck it? Also I have no interest in the 5xxx series right now or DX11. I plan on keeping the 2 4890's for awhile.
What resolution are you running at? Unless you are at low resolutions the graphics cards will be the bottleneck on the frame rates not the CPU. CPU bottlenecks are rare at resolutions of 1920x1080 and up.
Right now I am using an older Samsung 1440x900 Monitor and I also use a 37" 1080p television. I am going to be purchasing a 1920x1080 screen around 24" as the 37 is way to big and gives me headaches. I wanted to go CF to keep my FPS up when I bump up the resolution to 1920x1080.
It'll depend on the game, but that 750 @3.2 will be a pretty even match for the two 4890s. This is assuming you leave turbo boost on, if you have it off, I'd imagine the CPU would fall behind the GFX by a touch in most games (ie. games dual and triple threaded).
Do you get decent frame rates on the 37"? Are you entirely sure that you even need the upgrade anyway?
4890s we're built from the ground up for over clocking without needing to chug extra voltage into it. I'd also see how far your card will OC before you make a decision about getting a new card.
If a 4890 is equal to a GTX275 and a 275 is 15% slower than a 285, and a 5850 is 10% faster than a 285, it stands to reason you'd need a 25% overclock to be in next-gen level performance. If your card is one of the ones that make it up to 1GHZ while staying stable, you can bet you wont be needing a second card for 95% of games.
The i5 has a single pcie 2.0 lane. split to 8x for each card leaves you at almost exactly the max bandwidth for a 4890 at stock speeds. Pushing the memory at all will begin to bottleneck the 4890s. Odds are you wouldnt notice it at all, the framerate gain from overclocking wouldnt be noticeable when your already pushing 100+ FPS with Xfire. Any newer card with a higher bandwidth will be hampered more noticeably as the total bandwith is held back by the 8x lane. For now though, you should be fine.
mcnugget- I have been looking at those articles in regards to the split PCI Bus on my P55. The thing is most of them seem to show that there is a negligeble difference between P55 and X58 and unless you are running a x2 card the bandwith of the slot isnt saturated.
I have clocked my 4890 up to 950/1100MHZ with no artifacts so far.
I have not played a whole lot of games on the 37" because it hurts my head but I did have to turn off AA and AF in a couple of games because the performance hit was to much(Crysis and Mass Effect).
Anyways its nice to know that the CPU should not bottleneck them. Once the 4890's drop a bit ill have to snag another.