6970 or 6850x2

2 6850's

good question... 2 x 6850's will cost about the same as a 6970...

yes, your PSU will support 2 x 6850's. However, if you're overclocking the CPU lots... have many HD's, etc... you may be pushing its limits in the long term...

if it's a simple setup... with minor, or no overclocking... 600w should do it no prob... and the Crossfire 6850's will highly outperform the 6970 single card.

2 things to consider though:

if a game you play doesn't support Crossfire - you'll be cut down to a single 6850 cards' ability

2nd - is the Radeon HD 6950 2GB card option... save a $100 -> and (easily) flash its BIOS to a R6970 for free... then down the road... save a little more... upgrade your PSU and get another 6950 2GB...

I say get as much as you can in a single card now and crossfire later when the price comes down. Go with the 6970s. You'll sacrifice a bit now, but 2 6970s later are better than 2 6850s later.

Plus I've had so many driver-related issues over the past year with my crossfire setup, I'd wait until you know these are cleared up (I traded my Crossfire for SLI I was so fed up). My single card AMD setups have all run with no problem. I'm sure you'll be quite satisfied with the single 6970. The 6970 will give you 60fps minimum at 1900x1200 in most games with just about everything maxed. You may have to turn down the AA a little, but it's still good quality video at playable framerates. Plus it has 2GB of RAM so you'll be ready for a multi-monitor Eyefinity setup if you so choose to do that.

If you do decide to crossfire later with the 6970, make sure your power supply can support it.