[chumbucket]

Pipe_Dream, welcome to the site. I think Fugazi is the only member on board that has repowered with a 4 stroke motor. He went with the Johnson/Evinrude badged Suzuki 140. At last report, he sounded fairly pleased with the performance.
The only reports that I've heard from a few people I know with 4 strokes is that the power in the midrange seems to be a little lackluster. It probably wouldn't be an issue for a 200 hp on a V20 though. I haven't looked at the numbers recently but what are the weight differences between the 200 HPDI and the 200 4 Stroke? Could be a factor.
Although mine is and older motor ('89), I have a 2 stroke Yamaha 150. I really get super performance from this motor and would consider repowering with the same new version of this motor in the future. It's quiet (really, it is), economical, and delivers good top end and cruise speeds. That's just my opinion though.
I'm sure others will chime in with some good views on this as well. Best of luck in your decision making.