We need a sticky on what a bottleneck is sooo badly...
If you are gonna spend that much cash on video cards you owe it to yourself to spend a lot of time reading up on system design. You should be the one answering questions if you are enthusiast enough to build a rig with gpu's like that 😛.
Anyway, yes it will bottleneck a bit. No, it won't bottleneck enough (almsot nothing actually would) to make the 285's in SLI anything but the best dual GPU setup you can run. If you are spending that much cash price/performance must not matter all that much to you (which is fine).
Will you get as mcuh FPS as someone with an i7? Absolutely not.
Will you get more performacne that you would out of any other double GPU cofiguration? You sure will.
Computer bottlenecks are not hard, and they are not linear. There is no magic point where a gpu all of a sudden doesn't give more performance as it gets faster (well.. there is eventually if we talk about cpu limited settings where you effectively don't use teh GPu at all) You simply get less and less out of it. Frankly if you bought 285's in the first place you probalby don't care about the diminishing returns anyway as there are FAR better ideas price/performance wise. I would assume the fastest is what is important to you, not how much faster. Obviously if how much faster is important you might need an i7.