I've been thinking that for a while. Consider these players, who could probably all slot within the top 30 or so.*
Black 5'10"
Quero 5'11"
Valerio 5'5"
Chourio 5'11"
C. Rodriguez 5'8"
Wood 5'10"
Moore 5'8"
Lara 5'7"
Arienamo 5'8"
Guillarte 5'11"
O'Rae 5'7"
Norman 5'8"
Baez 5'9"
Ereu 5'10"
DiTuri 5'11"
* I don't think being 5'11" is limiting at all, unless the player is a 1B exclusively. My suspicion is that for players < 5'10," their ultimate ceiling is lower (on average) than their performance at the lower levels of the minors would suggest (say you have two guys who are legitimate prospects and are hitting about the same in A ball, and are the same age--I'd expect the 6'1" guy to end up the better MLB player instead of the 5'8" one). Exceptions will continue to exist, of course.
And, of course, 5'10 is fine for a C or middle infielder.