How long to reach top speed

[thebottomfish]

I'm using a brand new omc tach so I'm really hoping that's not it, I might get one of those tiny tachs as I hear they are pretty darn accurate just for testing purposes.
I have tried a 13.75x17 ss prop, 13 7/8x15 aluminum prop, 13.75x13 ss prop, all 3 blade props and they all read 5200/5100 rpms
I rebuilt The carbs at the beginning of the season, new spark plugs link and sync and fresh lower unit oil
The boat is not waterlogged as far as I can tell, this 32 top speed and top rpm is whether I have 4 people and a cooler and full tank or I have just myself and no gas, I might lose 1 mph or so but it's pretty dead on and that's according to gps i don't have a speedometer

The gw was a 21 walk around with a 175 johnson of a similar vintage...I just guess I didn't expect that much of a difference with 35 hp and a similar boat, he also tops out right at 40mph