If you were going to be getting the 1GB Sapphire 4850 that you linked, then you're better off going with the 4870 you mentioned previously. I only recommended the 4850 that I did because it would save you $90 and you were looking to decrease the price.
I wouldn't be the one to ask on 2x 4870s, but I did do some looking around. There do not appear to be any single slot 4870s. I'm seeing rumors that ASUS made one, but I can't seem to find it, and all the others appear to be dual slot.
It appears that the board you've selected (as well as other intelligently designed boards) would be able to accommodate two 4870s, but bear in mind that you will essentially lose one PCI slot (on that board) by doing so. I would echo Adama's sentiment of favoring Gigabyte, but again, virtually any equivalent suggestion I can make will at best save you $15 or $20 and may in fact be more.
If you'll look back at my previous post, you might recognize the fact that I recommended a beefier PSU if you intend to run significantly higher graphics in the future, which you appear to be considering with your mention of 2x 4870s. If that is the case, I'll be glad to recommend one, but do note that the one that you've linked is most probably going to be insufficient for that purpose as well as the one I've linked-and you just can't find a PSU that "heavy" for much less than this, and to be honest this would be preferable, depending on how much upgrading you intend to do with this system and how long you intend to keep it.
I may have gone slightly overboard on those suggestions, so if someone who has more experience running the higher end graphics cards would care to comment, that'd be helpful-I'm only running an x1950GT, so I've never worried about my power consumption, at all. However, it definitely leaves you room for further expansion in the future.
The CM is very good, but it's going to be running at or near its 12V limit with an OC'd C2Q and 2x4870s, at high load at least. If you don't intend to OC or don't intend to play games that stress both your CPU and your GPU(s), then this is less of an issue, but it's still worthwhile to look forwards and consider what you might upgrade some components to.
The idea here is that you should only have to buy your PSU once. There's no point in buying one now and 6-12 months down the line buying another one so that you can run another video card in tandem with whatever one you get now; just get the "right" PSU first. There is of course the little problem of companies changing what power plugs are needed for their cards, but adapters are normally sold relatively shortly after these things happen and to be honest I think we've seen the end of this for at least a little while with the 8-pin connectors. You may also notice that both of the ones I've linked in this post have 2x6-pin (for running 4870s) and 2x6+2-pin (additional optional for 4870 or for running future graphics cards on 8-pin).
With the Nehalem cores out, CPU prices will be very different in a month.
Hopefully and relatively likely (though not necessarily probable). We'll see. In any case, the Q8200 he's selected is only $190...how much lower do you imagine it will go? This is a serious question, by the way-I'm curious what your estimate would be.
I'm doing the best I can to keep him under budget (though it's looking worse). If things change by the time he buys, he can take that into account, or perhaps ask for milder suggestions.
Exactly. The Core i7 will probably be much more affordable then. It's designed for the DX10 games, so if this is an investment...
Let's do a short component comparison.
C2Q: $190. LGA775 CF motherboard: $100-$130. 2x2GB DDR2-1066: $70 (that's a suggestion, Thrawn). Subtotal: ~$350-$400.
i7 920: $320. (This looks bad already.) LGA1366 CF motherboard: $300+. 3x2GB DDR3-1600: $300+. Subtotal: $920+.
Difference: $500-$600, give or take. That's going to decimate his budget. If DDR3 came down and the LGA1366 motherboards dropped below the $200 range, I could see it being worthwhile, and honestly I see where you're coming from, as moving off of the FSB is a Big Deal, but I still can't recommend it under the circumstances.