Video editing is very good, Photoshop won't quite be up to par until it is Universal (although I can't give a first person account of this, I don't have Photoshop). Definitely very good for video editing though.
A friend of mine still edits video with a Powerbook G4, 1.67, 512 MB RAM (I think), so, I guess that the new iMacs will do just fine but if you really want to make sure and you have money to spend, go for the Mac Pro