Ginn ran his lowest at 4.32 at the combine and his adjusted was 4.38. Percy Harvin clocked at 4.41.
Hyde's combine doesn't tell the whole story because he tweaked his hamstring but he probably wasn't gonna run above a 4.45, if that. Smith will put up similar numbers, likely in the 4.50 range. That's still plus speed for a RB of their sizes, but RBs just aren't putting in sub 4.4 times because of the muscle they have to have to survive the physical stress of the position. Chris Johnson ran in the 4.2s in 2008 I believe, but only those in his mold and athletes like Dri Archer will run that low as RBs.