Really that much difference?
Well, here's what I've got: '86 model 225 G, Honda 225, dual batteries, tabs. None of the older models are dry rides compared to newer hulls, regardless of engine. The extra motor weight places my scuppers at about the water line at rest. With just motor trim I can make it ride high enough to beat you senseless or low enough to bury the bow in 3'ers. With tabs, it's a simple matter to tweak the ride for max fuel economy and/or ride. My transom is dry, the bracket is fine, and I wouldn't want anything less than a 225 (can't speak to a 250, but my 225 weighs 680#). I also can't speak to the ride with a full aux tank (would be to the rear in my boat), but I believe I would have enough motor/tab trim to handle just about any weight distribution.
That being said, your 228G is the same hull and it's more bow heavy than the T-225, so your scuppers shouldn't be an issue. If your transom is a problem with a 4s, bet your a** it's a problem with a 200 HPDI. Ditto a corroded bracket. While it behooves the owner of older hulls to know for sure, not all older Gradys have wet transoms, corroded brackets and leaky fuel tanks, popular misconceptions not withstanding! I also checked with Grady, and they said the transom/bracket were more than adequate for a 225, all else being equal.
I often add a bait well at the rear bulkhead that weighs 280# when full. Only with 2 grown men in a corner is there any scupper leak (I actually use one of 'em as a bait well overflow), and it creates nothing unusual as far as getting up/maintaining plane or ride characteristics. I also usually trailer, so scuppers aren't much of a consideration anyway. Fully loaded I cruise at 4200, 29.5 mph by GPS, right at 3 mpg in nominal seas. Any wave I'd take over the transom would damned sure swamp a notched transom (not sure how that got into the conversation since you don't have one), and anything over the bow would would be the same difference with any engine.
The answer? Go with what makes you and your wallet feel good. I can tell ya a 4s will be marginally cheaper to operate and certainly more pleasant to be around while cruising. If you want to really know for sure, find someone with a 4s and offer to pay for a ride. New or old hull, you'll get a good idea what yours would do .... :wink: