Re Power

[sidelock]

I have an SF 18 with a 1998 Yamaha C115 that I'm thinking about re powering come spring. The motor has been very reliable and trouble free thus far and this past summer I had it compression tested and the mechanic said it read an even 120 across all cylinders but sooner or later its inevitable that it will have to be replaced.
The Yam. C115 weighs 330 lbs. and I'm trying to stay as close to those numbers as I can for obvious reasons.
According to factory specs here are the weights of the motors I am looking at.
Yamaha.....F115....weight.....377 lbs.
Yamaha.....F90....................366 lbs.
Merc.........115EFI................359 lbs
Etech....... V4.115................390 lbs.
Etech........E90DPX (inline)....335 lbs.
Etech....... E90HGL ..............390 lbs.
Would there be a big performance difference between the Merc. 115 HP and the Evinrude 90 HP since its a two stroke compared to the Merc.four stroke ?
My mechanical knowledge and experience is very limited so any insight on the subject would be greatly appreciated.