Depends on potential, practice time, playing time, starts, number of games. Having said that, the 33 spd is not going to grow higher than the 51 spd (unless he is STL and the 51 spd guy is low potential).
If they are both high potential, I would expect the 67 WE guy's spd to grow by 5 ish points per season and the 48 WE guy's to grow by 4 ish per season.