Though I've still not decided what to do, I wanted to post the results of my simple test/observation on the boat today.
First, here's a new one to me and maybe to some of you: the scupper exits are actually underwater at rest, from the factory. The drains in the cockpit are well above the waterline (because the whole cockpit is), but the rubber valves on the transom are much lower than those and sit in the water.
Second, a dealer visit. Every GW I saw had a four-stroke on it, and the weight balance doesn't appear to be significantly different than my boat. Sure, the SV2 hull rides different, but the overall balance and layout are very similar. Plus, they had multiple boat versions with the same hull, with vastly different weight balances (cabin or no, hardtop or no, some hulls allow singles OR twins, etc.).
Third, the test. While at rest in the water, I had my wife measure down the scupper holes in the cockpit to the water level while I was at the helm. I then moved my 200-lb body to straddle the current outboard and had her measure again. When moving from the transom to the top of the motor, the water level didn't change at all. When moving from all the way at the helm to the top of the motor, the water level in the scupper holes did come up about a half inch (still several inches below cockpit level).
So, the conclusion is that the doomsday visions of the boat being wildly out of trim and being unsafe with the weight of a four-stroke out on the bracket are bunk. The net gain of the 4S is likely to be 60 - 70 pounds (max of 100 if you don't count removing the oil tank), and I put a full 200 pounds back there with very little change in the boat.
Now maybe mine's a litttle more forward-biased than some, since I have a full fiberglass hardtop, rocket launcher and radio box all added above the cabin, but it still seems like a minimal change on a 6000-pound package.
As I've said, I haven't made up my mind, but I'm definately not ruling out a four stroke due to the weight issue (speculation vs. my test and owner reports).
I agree with the comments that a F225 might be disappointing performance-wise after the EFI two stroke, from many comments I've read. However, I've read good things about the F250, and it's only around ten pounds more F225. So far, it looks like it's down to a 200 HPDI (again, lots of great comments) or F250, and will depend on the right deal.
Again, thanks for all the replies and spirited debate! I always learn a lot from this forum.
