Prop question

[Captdj]

Ok so I switched the prop over to the 18.5 my cruise speed came up like I was hoping. Now I am wondering if I should raise the motor 1 hole. Right now it is mounted one hole down from the top (next hole would mount it as low as possible).
Crusie- 35mph at 4300-4400.
WOT - 44mph at 5800
This is with 2 adults and fuel of fuel, t top, and full curtains.

Switching from the 17 to the 18.5 I gained crusie speed and I am around where I want to be, but I lost on the top end. Knew the RPMS were going to drop, but didn't expect to go from 6300-6400 to 5700-5800. Now I am wondering if the motor shouldn't go up 1 or 2 holes.

Boat again is a 2001 Seacraft with a 300 zuk mounted to transom no JP or bracket 30 inch shaft