Core i5 - 4850 Crossfire/4870 OC'ed/4890?

Ok so I'm planning a Core i5-750 build with one of the better motherboards (ASUS P7P55 Evo/Deluxe) and 1033MHz DDR3, my question to you guys is as to which graphics card I should go for? I'm aware of the threads advising to hold off and wait for the 5xxx series but my budget won't stretch that far + I'd like the machine sooner rather than later.

The current Sep '09 Best g.card for the ££'s recommends 2x4850's in CrossFire at the price point I'm looking at however I'm abit concious of the power requirements of a crossfire rig + with GDDR3 would I be correct in assuming these cards won't hold up so well going forwards? The 4850X2 is also an option however it's price quickly catches up with a 4870 and I'm assuming the single 4870 may outperform it? (Single-card CrossFire/Sli cards seem an intuitively bad idea to me - heating must surely be much more demanding + impact their lifespan, no?)

Next up is the 4870 - this would be ideal if it's possible to OC to be comparable to a 4890 as it'd save a few tens of £'s I can put into something else. I've read that the 4890 is just a stock OC'ed 4870 anyway, in which case I don't see any great advantage in shelling out a little more.

If you could make any brand recommendations that'd also be really useful, I hear the Sapphire 4890 is one of the best around and so I was considering:http://www.google.co.uk/products/c [...] sa=title#p.

Thanks for any help you can send my way,
Cyrl

4890 and overclock it yourself.

The 4870 probably won't OC to 850mhz without volt mods and very good cooling. Mine only does 810/1150 with a small volt mod and stock cooler. The 4890 can typically get 900-950mhz when overclocked. It also idles at much lower power than the 4870. If the price isn't much higher, then I'd recommend getting the 4890.