smaller is better for accuracy/consistency. bigger is easier to see through fro low light situations while hunting. if you just like to shoot in the backyard and hunt i would go with a larger peep. if you are shooting spots or 3d the smaller (you can see through) the better. if you like to do both, its best to just find a happy medium and figure out what is the smallest you can use, but still see in low light.

as far as speed... what is 1-3fps difference. that is nothing compared to the added benefits of a proper (for you) peep setup. speed should never be a determining factor in teh accuracy/consistancy dept. its always better to shoot better than faster. a fast miss is still a miss...
Derek