Well, sounds like the 640 just isn't a good 3D card. But apparently it seems to be quite a good HTPC card:
http://www.anandtech.com/show/5969/zotac-geforce-gt-640-review-
So yeah, I wouldn't suggest this card on anybody wanting a cheap 3D card. But if you're going to use it for other things...
Yeah except that last gen (and probably gen before that too) Radeons beat it in HQV too, even some of nV's older cards beat it in HQV.