The 5d Mark II is better. It has much lower noise at high ISO, significantly better image quality, much better color depth, much larger sensor, weather sealed, significantly larger viewfinder, higher true resolution, slightly more dynamic range and better boost ISO. The lenses do matter but the 5d Mark II has more pixel density, as stated by an answer above, which means it can absorb more light and hence would give better quality. Read this review for it to get more info for it by an actual owner:
http://www.amazon.com/review/R1HX72PT9KPNWX/ref=cm_cr_pr_perm?ie=UTF8&ASIN=B001G5ZTLS&nodeID=&linkCode=&sourceid=md.ds&tag=famaeim-20
You can look for the price details etc here:
http://www.amazon.com/Canon-EOS-5D-Mark-II/dp/B001G5ZTMM/ref=sr_1_2?s=electronics&ie=UTF8&qid=1323328714&sr=1-2&sourceid=md.ds&tag=famaeim-20
To compare the two, read the specs and other details of the 7d as well:
http://www.amazon.com/Canon-EOS-7D-28-135mm-Standard/dp/B002NEGTU6/ref=sr_1_2?s=electronics&ie=UTF8&qid=1323328718&sr=1-2&sourceid=md.ds&tag=famaeim-20