I have a 96 248 Voyager with a hardtop and an 02 Honda 225 with 600 hours. With a 15-1/2x15p prop I turn 6000-6100 RPM and can see 42mph on a good day with the right sea conditions. The Hondas like to be in the 5800-6000 range WOT. These Hondas wind up pretty good when the Vtec kicks in. Things to look for; Check the mid-shaft bushing on the driveshaft (plenty of info online if you google it). Its a yearly maintenance item to grease thats may not be in the manual. There is a VST drain that located on the starboard rear of the VST tank. Good to drain periodically if the screw is not seized. Change the high pressure and low pressure fuel filters every season as well as drain the fuel water separator. I remove and clean my VST yearly (especially the fine mesh screen under the high pressure pump); My motor hates ethanol fuel, not sure where you're located, but if you can run ethanol free thats a plus. Startron and ring=free with every fill up. I run a 2 micron fuel water separator on the boat also. Replace or clean the thermostats, and replace spark plugs yearly. Water pump I do at 200 hours.
Visit Marineengine.com, lots of Honda info there. Good luck with the new rig, the Gulfstream is a sweet ride!