Both can crush him in a foot race, and yet, neither could hold Austin Carr's jock as a WR. OverInvestedCat's point is spot on. And the idea of size being an issue with football speed, you must be joking. How many 5'9 speedster WR's have gone through the league through the years? Steve Smith. Wes Welker. And 5'6" Darren Sproles deserves mention since he's probably as successful as a pass-catcher as he is a RB. And is 5'8" Barry Sanders unable to translate his raw speed to football speed because of his size?
There's a lot more to being a WR than pure speed. Speed isn't even absolutely critical (though of course it is helpful). Get a WR who can win jump balls, run great routes, and most importantly catch over someone who runs fast any day of the week. Miles Shuler contributed, but I would rather he were slower and could catch better. Perhaps, an investment in an automatic tennis ball machine or 10X more time in front of one would have helped him.
Speaking of WRs who lacked speed but had other more critical attributes to make up for it, for as much crap Kyle Prater got from some people for his lack of speed and "underwhelming" career, he was still our leading WR his senior year and if every WR does as well as he does, we'd have one of the top units in the league.