The radeon 5830 and geforce GTX 465 are failures, best avoided.
How so?
They are both built with reject chips from the top end cards with half the shaders disabled. This means they got all the worst bits (power usage, cost, noise) with none of the best bits (performance).
The 5830 is only slightly faster then a 4870 - a 2 year old card that cost about £100 a year ago.
The GTX 465 is a bit quicker (although no faster then say a 4890) but costs a lot (£200ish) and requires almost as much power as a GTX480.
The GTX 260 is a bit different. It uses a new design of fermi and a new smaller chip - built to be an upper mid range graphics chip, not a monster gpu compute one that can also do graphics. Check out the reviews - there are lots of them.