I'm building a 550 hp 500 tq engine that I need to figure out what prop pitch to start with. I'm going to need the engine to spin around 6000 rpms. I'm planning on using a Mirage Plus. Any suggestions.

I'm running a 502 and see around 67 MPH or so. I just found a Mirage Plus 23 that I think is going to work out. I'll let you know after testing. The boat had a 24 Bravo1 at one point and that prop worked well also.

How many HP is your 502?

6000 is a lot of RPM, should be interesting.
For reference our old 242 LS with about 525 HP would run between 70 and 74, depending on weight, with a cupped 23 Pitch mirage plus @ 5300+ RPMs. Also, was running a 2" shortie drive in the end. Before and after the shortie the 23 miage plus was what always worked best. I'm not sure you'd get close to your RPMs with a 21 mirage/mirage plus?

The engine was built local by the previous owner. I have been told that is just shy of 500hp.

I've got both a 19 and a 21 Mirage. I guess I'll keep them both for now. I was thinking I may need a 23 but at 6000 Rpms that seemed like a lot of prop. What kind of gains did you get with the 2" shorty?

I was thinking you may need to go with a gear change to get a good prop combo to 6000 RPMs, others may have an opinion on this. As far as the shortie drive, I noticed the boat rode flatter and I picked up 1-3 mph depending on conditions. Big waves required a 4 blade prop. I'd do it again for sure.