IMO just pumping more ponies without raising the X you are looking for a problem, until you get your gear case fully clear of the water you will encounter more and more stern lift a speed increases. The point will come where you will get unintended bow steer, that is a very freaky thing at high speed. continuing with your current power but raising the X to 17-1/2 will eliminate that condition and add 4-6MPH. It is a shame none of the experimenters got to see Steve's 18 run, stock 300hp Merc it ran 79 at its best. You guys are not much faster with a lot more power! With the power you guys are making you could go a lot faster and ride on rail road tracks with excellent control. Doncig went the power route roughly 500hp and only went a few MPH faster than Steve's 300hp 18, Do surely would have made close three digits setup correctly. I can more than understand not wanting to mod the boat and build a raised hatch, but you will never achiev the full benefit of the drive and end up with edgy handling at WOT.
No matter what your beliefs are "GOD BLESS AMERICA"
Fully retired marine tech near 60 years in the biz.