SeverCD (guy right below me) hit it right on the head. Only thing I have to add to his great reply is about scavenging. It has been stated by Ubisoft Devs that scavenging does not affect drop rates at all. It affects qualities of dropped items. For instance, you have a flat % rate of high end drops that cannot be altered. The difference between a guy with 20% scavenging and a guy with 200% scavenging is the guy with the high scavenging gets better yellow drops (they both get the same # in theory) but one guy gets mods and weapons/armor with crap rolls, while the 200% guy gets decent quality items more frequently.