Wow, if the Radeon 4890 is matched by the GTX275 that's a real hit to AMD, considering the 4890 is suppsoed to be AMD's top of the line.
EDIT:
At that price I'd seriously consider a GTX275. I just hope I can find it at that rate over here in the UAE.
I am pretty sure you will be able to. At most you will find it for $300.
But it isn't their top of the line. The 4870X2 is about $450 and is their "top of the line".
It isn't really a serious hit because both cards are priced at $250. At lower resolutions, the 4890 and the GTX275 take turns 1uping each other, though the 4890 seems to win a bit more, albeit with slight percentages. It does lose consistently once the resolution is past 1680x1050... but most people don't have monitors of that capability.
Overall, it is being considered a win for ATi, because the well priced fast product has forced NVIDIA to release a new product.
Keep in mind that when the GTX280 came out, it was priced at $550. When the ATi 4870 came at $300 and offered a great performance, Nvidia were forced to slash prices. Later, Nvidia released the GTX285 and the GTX260 maxcore, both which were more refined versions of the GTX 280 and the GTX260 respectively. They both were on a smaller manufacturing process, and thus were cooler, faster, and less power hungry.
The GTX260 maxcore from BFG was a real bargain. At $200, it wasn't very far behind the GTX280.
Anyway, if you have a 7900GTX, then one of these cards will be a good option... but keep in mind that this is the final refresh of these products. Both companies will have the next generations of their cards along in about six months. I'd suggest that if you are looking to upgrade, then you buy NOW, so that you can enjoy the most out of these cards. If you plan to wait three months, then you might as well wait three more. Though with the economy the way it is, we might have to wait even longer than six months for the next gen... so who knows?
I am personally finding it really hard to wait. My 8800GTX has served me well, and can make do... but I want one of these so badly.
edit:
It is also a win for ATi because they already have their product out there in a worldwide launch. The GTX275 will still take a week or so.