Wise of you to ask the club for help. They are a great resource, friendly, and helpful. You also have the beauty of a Merc a lot of people have experience with your motor and performance part are available.
I have a 73GT160 it came with a Johnson 85hp and was very useable 43mph by GPS with two adults.
I to have the quest for speed. Now have a 120hp Johnson. Prop SS22Raker.
First test run motor mounted on top hole. Results: Good 0 hole shot time, Hit the throttle and go no plain time, 52mph one adult, tight 360 turns no cavitations, throttle on throttle off boat would stand almost straight up on its tail (an entertaining trick). Bad boat trim only 50% useful 50% dangerous at high plain boat bucked side to side so violently it threw me out of the seat. Also used to much gas 12 gallons on 3 runs on my small test lake.
Second test motor raised now on second hole. Very happy with boat. Good: trim about 95% useable 5% wild. Perfect Hot Rod, fast and usable. On high trim exhaust note changes steering actually locks. I cannot turn it boat, straight ahead fast. Test on Mississippi distance at least 3 times the size of my small lake mostly WOT only used 7 gallons of gas! Bad some time to plain but acceptable and faster than plain time with 85hp. Also some cavitations on tight high speed turns. Again acceptable just have to remember to trim boat down on turns and up on straightaway?s.
Bad dropped GPS in water!
Happy with boat but still have the quest for speed. At some point I realize the speed will reach the limit of the haul design. Then I will need a second Glastron.
Plan: tune engine, check RPM, to see if I can try other props.
Have fun with your set up, it?s part of boating.