So now im fairly happy with my lens set up exept i hate having to change lenses to go longer, which i dont use often. So im looking for a little better IQ for my walk around lens (28-75 is decent just not enough compaired to the 70-200 and 50mm). Ive been wanting IS and have been lusting over the 24-105IS for a while now. So I rairly use my 70-200 f4, and when i do its more of the shorter to mid range of it (around 70-135). So question is will IQ be on par or better with my tamron 28-75 f2.8 and in between the 70-200? Im not to worried about loosing the stops from the 28-75 because the 5d has great higher iso compaired to my 50D and i have a 50mm 1.4, plus the IS will help with shooting at a slower speed(i rairly shoot fast moving objects). So what are your thoughts?