2G or 1G Radeon HD 5870.

[SD57]

Is there any difference?

[[Tycho]]

Is there any difference?

Yes. 1G will draw a bit less power.

[SD57]

And in performance?

[[Tycho]]

And in performance?

No.

[SgtSpike]

No difference in performance for hashing, some difference in performance on games, particularly at higher resolutions and higher AA.

[allinvain]

Get the one that is cheaper! But make sure in either case to underclock your memory (VRAM) to 300 MHz or lower. This will make a noticeable difference in the cards overall power consumption (20-40W typically. for me it shaved off 40W!)