Agreed. If 450hp is the max rating for your hull, I'm not sure if I'd want to go above that, but that's your call as it's your boat and the liability is on you... so to speak. I think part of the equation for max horsepower is definitely the horsepower level itself, but I think the bigger part is the weight of the twin motors. Although it seems like several outboard manufacturers, like for instance Yamaha, have the same weight for their F225 on up to their F300, as I assume they use the same motor/block but just de-tune it for the lower rated hp motors. Same goes for Suzuki, Honda and so forth. So I'm not sure why you couldn't "in theory" have twin F250's as opposed to twin F225's as they're the same weight. But as has been discussed on here before, Grady White's aren't exactly speed boats or designed for going as fast as possible, so I think that going with more power is just going to cost more in the long run without really that much benefit. If 450hp is/was the max hp rating back in 1998 then I'm thinking that should be more than enough for you 20+ years later