Correct prop size?

[Sredd]

Just purchased a 2006 1900sr with 5.0l merc. Want to use mainly as towing people for wake boarding and playing on tubes. Not too concerned with top speed(which at this time is around 43mph on speedo and gps) at approximately 4100 rpm, which seems low for wot. The prop that is on the boat now is 14.25x21x3. Wondering if this is the stock prop? Haven't had a boat in a while but last one was Malibu sunsetter. I know there is a big difference between the two, and the way they act/ride. Was thinking of trying either a 14.25x19 or 14.5x19. Was also wondering if I should drop down to 14.5 x17(or is that too big a jump). Which would you guys suggest for quicker hole shot? Boat seems to take a long time to get on plane guessing about 6-7 seconds is this normal for this type boat? Input would be greatly appreciated.. Thanks.. (First time poster and new to site).