Funny how times have changed, when i got my first rib it was a 5.2 meter with 50HP. Then a 6 meter Coastline with 115.
At the time both were not considered to be underpowered but relative to todays boats, it would look they were.
I remember a former poster here who put 200 on a 6.5 meter telling me that "ya dont have to use it all!" same boat has a 200 HO now on same boat so he like many of us are always after speed.
If your happy with doing 30 ish knots (which frankly compared to most other things on the water is pretty quick) then go for a smaller engine, save on purchase cost, save on fuel (maybe) and have fun with the money you have saved.
If like me speed is important, then fork out the extra and go bigger HP but thats a choice i take and reflects what i like to do with the boat. to say one is better than another is subject to how they are going to be used IMO.
sorry for thread drift. good luck with whatever you choose! im sure you will enjoy it.