Just for my own education because I'm trying to learn as much about this prop stuff as I can... I also have an 18' aluminum boat(heavy SeArk) with an Etec 90 HP, top operating range also at 5500 RPM, but a SST 15 pitch prop puts me right at the top of the RPM scale with a 3-4 second hole shot. What would account for needing to use such a difference in props other than maybe the weight of the boat? Mine also ran at the same RPM with the original aluminum prop.
2015 Seaark 1872 MV CC Etec-90
Two Helix 12 CHIRP SI's, , MinnKota Riptide ST80/i-pilot Link, Bob's Hydraulic
2018 Robalo R180 CC, Yamaha 115
Bitter Gun Owner