150 XP Performance questions

[speedo]

Greetings from a newb.

I have a 1991 Evinrude 150 XP on a 1991 javelin FS (17' 9"). Compression numbers were:
84 88
85 87
80 90

We had a defective compression gauge, so re-test was done an hour and a half after initial warm up and we only warmed it up again for 3-4 minutes, and neglected to advance throttle to WOT for the test.

I ran the boat with just me (225#) and 24 gallons of gas. At WOT, it had a fantastic hole shot and got to 45 mph at 3900 rpms easily, but rpms seem low.

I'm planning to take it in for an impeller replacement and am wondering what else I should have checked. (Tach calibration?)

Suggestions?

Thanks in advance,
speedo

[boats.net]

What were the new numbers, rule of thumb is must be over 100PSI and with-in 15psi of each other.