Both should be fine since Video Editing isn't very stressful on gpu's. However, the more powerful card in general is the ATI Radeon HD 5770 in this case.
depending on which program you use adobe premeire pro cs5 uses the nvidia cuda language to encode and generally speed up video editing so its a thought but the 5770 is generally faster
depending on which program you use adobe premeire pro cs5 uses the nvidia cuda language to encode and generally speed up video editing so its a thought but the 5770 is generally faster