Just an opinion, you should probably be on the 19, unless you have short legs for a guy who is 6'2". I am 6'4" and ride an xl.
29ers "roll faster" because the larger wheel size reduces approach angle to obstacles. If you have ridden a 26er before, you would probably notice right away.
Some manufacturers 26ers and 29ers will have the same stand over, specy is one of them I think. At least they were when I was shopping.