High five 21p five blade prop running 5000-5100rpm on 4.3 mercruiser

[BF2Martini]

Hi ! I'm new to iboats and boating in general. I have a 93 gw invader 18 ft bowrider with a 4.3 mercruiser alpha I in it and it has a stainless Mercruiser High-Five 21p prop. I'm getting 47mph at 5000-5100 in WOT. looking around this forum it sound like this motor needs to be in the 4400-4800rpm range in wot.
Me thinks I need a different prop for more top speed and better cruising. I can't find anything around here on the high-five 5 blade prop that I have, so what would be a good choice for more top speed and better cruising with this boat ?