Question nVidia Graphics Card

[Vanguard]

So I'm looking to buy a new graphics card, and I'm puzzled by the cost of some of the options. Question is, based on this:
http://www.geforce.com/#/Hardware/GPUs/geforce-gtx-580/performance

and given:
GTX 295 $290
GTX 480 $490
GTX 580 $580

a) Why would anyone buy a 480 over a 295, when they have equal performance and a significant price difference?
b) Is my best bang for the buck and performance not 2 x GTX 295's over a 580?

I'm going shopping this weekend and I'd appreciate your guys input. And please don't turn this into an ATI vs nVidia debate... don't care

 

[Lucy]

I recently did similar price matching, and there's an option you seem to have omitted: The GTX 460 is a solid-looking card at a similar price to most of the 2xx series cards I've seen (Google tells me £173.19 = $277.900674 at the moment).

As for the 295, they're good cards, but only DX 10, wheras the 4xx series are DX 11 cards.

 

[Unstung]

The 480 has a few more features; compare these specifications:
http://www.nvidia.com/object/product_geforce_gtx_480_us.html
http://www.nvidia.com/object/product_geforce_gtx_295_us.html
Not sure if they are worth it, though... I'm not even sure what "NVIDIA 3D Vision Surround Ready" is. The 480 requires less power, but you better have a pretty strong power supply for either of these.
Otherwise, I don't know much about graphics cards to tell where two 295's would be better than a 580. I only have a GT 240. You're planning on using such a powerful card to its potential?