Hi

I got myself a 1998 Fountain 29. It has one modified Mercruiser MCM-HP500. (Now 548 with 602HP at 6000rpm.)
Bravo One XR (I think 1.50)
Propel Bravo One 4 blade 15 1/4 x 26p Top speed with 4 people and 3/4 tank fuel. 69mph. But only 5300-5400 rpm. If I trim more to increase rpm, the speed goes down.
What propel do you recommend to get more top speed?

From the numbers you provided, your slip is around 20% which is poor. Are you sure the motor makes 602HP? 6K RPMs sound high for a marine motor too.

Have performance papers on the engine. Avg. 4800= 534,6 Min. 3600 =407,7 Max. 6000 = 602,3

Ditch the people, you'll likely see faster speeds at same RPM, decreasing slip %. Even further, you'll probably turn faster RPM and better speeds.