welcome, it's always good to have another powerboater up here, hopefully we'll see you on the water this summer!

as for your question, i'm not quite sure what your asking. if your wanting to know a starting point for your jetting, i'm sorry i haven't ever jetted a combo just like yours, but i don't believe your TOO far off. i can tell you the air density here compared to 600' elevation is going to be about 14% less (600'=14.38psia, 4300'=12.36psia). a couple sizes smaller should put you real close.

P.S. just a word of advice; don't try & meet up with nordicheat at the lake, he just avoids people. LOL

Yup!! Especially when they're broke down

The rpms and speed with the 23" prop at your altitude look like they should. Propslip is right where it should be at 12%. I see no reason to go down in pitch. Going to a 21" would turn too many rpms. Jet the carb down for your altitude and you will probably gain a few rpms.

Any experience going from a mirage 23p to a mirage plus 21p, I under stand there is more cup in the 21p in the plus series.

I didn't nitice that your prop was plain Mirage 23. Pitch for pitch, the Plus spins about 200rpms slower. Speed is the pretty much the same. Going from your Mirage 23 to a Mirage Plus 21 will probably give you about 200 more rpms.

I have a 98 260 Powerquest. I have a 21 Mirage plus. I tried my friends 23 Mirage and turned the same RPMs, for the same speed. A lot more slip with the plain Mirage. I have a 454 mag Carb motor. At sea level in salt I turn the 21 5050 . I just had it repitched to a 22. I did try a 24 Bravo 1. I could only turn that at 4550. But I did like the midrange. I thought the Bravo 1 gave me pretty good bow lift. But that prop was worked a bit by Spinnelli. Our boats do have a hook that seems to limit top speed. I think this boat requires 25 hp for each MPH gain

Hey bsc,
As Griff mentions, if the 21 Mirage+ turns 200 rpm more than the standard 23, it would probably put you right where you want to be; 5250 rpm. Considering the 60 degree weather you tested in, it will give you some cushion when we get up to our normal 90-100 degrees.
Should be a good place to start and then you can have it labbed to fit your needs perfectly (if there is such a thing in the prop world).
Later,
Dave