Replacing a 8800gtx, crossfire? sli?

Hi folks.
Have finally decided to replace the ol' 8800gtx with something new.
Still playing anything i throw at it at max settings but i am starting to notice a few annoyances now, like GTA 4, it plain refuses to hit max settings due to the memory of the card hitting it's limit.

So here's the question, what should I replace it with.....

Current setup: Asus Maximus Formula motherboard (crossfire x38 chipset)
Q6600 @ 3.2 Ghz
8gb Dominator 1066 DDR2
Enermax Liberty 500watt psu (can replace if needed for new graphics setup)
XfX 8800gtx (xxx edition)
22" widescreen monitor (Dvi etc etc)
Various hard drives, disk drives etc

My last card was a 1900xt (the original 512mb version), then i jumped back to Nvidia for the DX10 support about 6 months after it came along.
So i have no issue with using ATi or Nvidia, if it's nvidia though it's going to have to be a single card since i don't have SLi on this board.

Was looking at the new 4770 in a crossfire setup but not entirely sure it's going to be a decent jump in performance.

Budget, anything up to £165 per card if crossfire (since i can buy 1 a bit later) or £300 if a single card.

Thanks people.

dual 4870's?

they cost about £155 each for the 1GB models.

or maybe a single 4890 because even that is slightly overkill for that resolution.

If you are considering 2 4770s then I am guessing that you can get a 4890, well get it. The 4890 will do about the same, but will overclock higher. You can also grab another down the road.

Edit: Also do not worry about GTZ IV, I can't even max it because it is such a terribly written PC port.