Since it was brought up... Figured it'd be good discussion to see the comparison. Pretty good, considering the Receiver Whisperer keeping him out of same games, and being suspended.
Also considering Brees/Warner/Cutler/Brady/Manning/Ryan/Schaub vs Brodie/Huard/Thigpen/Cassel. For most of that list, anyway. Cassel can perhaps be excepted from that list, given some OLine woes in 2009, and a complete lack of direction in 2012. We at least know he can excel with pieces in place.
Steve Smith and Megatron are obvious exceptions as well, to me, with Megatron having the largest catch radius I've ever seen, and Smith being possibly the best YAC guy I've ever seen.
I like to think Bowe would be upper echelon with a higher-quality QB.