I wouldn't even get the two 4890's, once again it's old tech. It may look like a great deal now (especially second hand) but I can guarantee you that you'll be kicking yourself when games start to support dx11.
If you're buying new then at the very least look at 2x 5770's (slightly less performance than the 4870, overclocks great) and bloody cheap or a 5850 (reasons stated above) and buy another later when they return to RRP or better after the nvidia releases.
QUOTE (R4n)
While I agree with you in theory, there are plenty of reasons to stick to Nvidia or ATI for features not related to gaming.
Also if you purchase items based on a price/performance ratio, then going for an outdated card can sometimes be a good thing, as older technology can be much cheaper
I do see your point but my view is a brand new 5770 costs exactly the same amount as a 4870 (and should actually be cheaper) and you're future proofing yourself for any DX11 game on the horizon. You would get a decent amount of performance straight out of the box and could possibly outperform a 4890 after tweaking due to less overclocking overheads (i haven't actually looked into it so take that at face value)
I personally run a 4870 at the moment and will upgrade soon. Thing is I will not pay for inflated prices and i'll willingly wait another couple of months to at least check out what nvidia has to offer. If they don't come to the table with something spastic awesome (that will no doubt come at a rediculous nvidia price

) then i'll probably just get a 5870 or a 5970.
In the meantime, i7 and 9tb in raid6 for me.