bitsamonkey has a late model zuke 90 on his 18 and gets 37 mph and 6.7 mpg at upper mid-20s cruise. Certainly not under-powered and exceptional economy. Terry england runs a 90 etec in his hardworking 19, and Fr Frank ran a 90 Opti on his Seafari, currently owned another regular, not sure if he repowered so maybe he'll chime in. While I'm sure they wouldnt hesitate to run more power, I've never heard any of them claim they were underpowered. I run an 83 115 tower of power ande it does about 36 and gets on plane instantly. My only complaint is fuel economy at hull speed.
The new merc sounds excellent in weight to horsepower ratio. Its only 20 to 30 lbs heavier than the etec and zuke with more ci and ponies. I like 2 strokes, especially modern direct-injects, but I cant argue with a 4 stroke that has cut considerable fat...did they leave out any parts
Another thing about the merc is that your controls probably swap right in.