<span style="font-size: larger;"><span style="font-family: Comic Sans MS;">On paper there will be a difference ... the 11x5 will draw less amps than the 11x5.5 ... however:

i. if you are particular so as not to over prop then the former prop will be what you want;
ii. some may want the revs but not the amps so they will settle with the 11x5.5;
iii. some may want a tad more speed so they will go with the 11x5.5;
iv. some motors may handle either prop better than the other so you test and get the feel you want;

If not it will hardly matter as long as your system can handle the amp draw. To each their own I guess.</span></span>