But I think you guys are forgetting that 4870 X2 are 2 GPUs slapped together, so it's power consumption could (by common sense it will) be a lot higher than that of the 280, unless Ati can do some magic this time around, which I doubt. I do think it will be faster, but I don't think it will do a lot better than 3870 X2 in comparison. << Note that this implies I'm saying it WILL DO better (overal or in the market, etc.), but not A LOT BETTER in terms of performance-per-watt. The X2 consumes more than the 8800 Ultra and a lot more than the 8800 GTS 512/ 9800 GTX, while not being a lot faster. It consumes more than 2xHD3870 and I don't think they can improve this situation by much in the next generation. Nv 280 consumes exactly 50% more than HD4870, so I don't think they can make the X2 consume less than 2x the power of a single card and that would make the Hd4870 X2 draw significantly more power than Nv's cards.
Then there's also the price issue. I could be wrong, but I find it hard to believe that costing the HD4870 more than $300 they can make the X2 cost around $500. Maybe (I'm almost sure really) they are counting with GDDR5 pricing going down by the time they launch the card, but by then all the cards are going to cost less. Specially if the reason for GT200 to be so expensive is that it has extremely low yields, as that's something they can fix "easily". They usually do (speaking of chipmakers in general).
Also later but soon Nvidia will launch it's 55nm refresh with the possibility of a GX2 regaining the crown. And sadly if that happens it will be an all-around crown because Nvida right now is a bit better in perf/watt and perf/price than Ati while using a bigger manufacturing process. 55nm will only make this fact more radical.
IMO Ati is going to be the better purchase option in the near future, as it's selling their cards within the hot spot, but we clearly can't count Nvidia off. According to leaked specs and bencharks HD4850 won't be faster than 9800 GTX so Nvidia has that card to fight against Ati. It will also have the GT selling for significantly less $. If HD4870 will be "better" than GTX 200 cards because its price, won't it be HD4870 < 9800GTX < HD4850 < 9800GT ?? IMO Yes. Where's the low limit? It will depend on the performance of the cards, and as it stands right now BOTH companies will have their products in different segments. They won't compete in performance, they WILL do in price/performance and there, the lower you go the better bang for the buck you will find. And that will be 9800 GT/GTX* IMO, but only time will tell.
* Because contrary to HD4000 series they won't be high-end and prices will be easier to lower to the desired point. Similar situation as with the HD3870 vs. 9600GT and HD3850 vs. 9600GSO.