Not sure what the label plate would indicate for max HP, maybe Gregg has a brochure. I would take a SWAG and say around 60hp is it's labeled max hp. Difficult question really, if you put the 50 on it, you'll always be wondering how much better it would perform with the 90. I suppose it comes down to your intended use, and maybe your insurance carrier's stand on exceeding label plate specs? Since I do my own rigging, I'd give the 50 a try, then maybe the 90. If you're having a company rig it, will they even consider the 90? Nice looking boat, I always like them with the split windshield.