he is faster than he looks out there because of his stride and size.
check out 1:21 of the video
also, RG3's 40time is with no pads on. Kap is bigger than RG3, so there is a chance that he is faster or just as fast on the field (wearing the pads). Also Kap ran that 40 at not 100%. I know excuses, excuses...but what is known is that RG3 is comming back from a pretty bad injury and we have to see if he still has the same speed. But I'm sure Tiburon still has him at 93.
but RG3, Russell Wilson, Vick all are more agile than Kap...no question there. But straight line speed, imo Kap is faster or just as fast as RG3. Also Vernon Davis said Kap is one of the top 3 fastest players on the team.