Firstly.. Where are you from ? I would guess QLD like me.. But you may or may not know that Stacer and Quintrex are made in the same plant here in Queensland by Telwater.
I own a new 460 Sunmaster sports so I am a bit biased towards the Stacers.
I have 50 ELPTO Mariner and It will push my boat to 30 knots in the Pumicestone Passage with 4 on board,and I think it has the right amount of power for what I want. (Some packages only have a 40hp)
Some things I learned : Make sure they set the boat up right on the trailer or the loader device wont work well. If you get a 2 stroke Merc or Mariner, keep an eye on the oil injection tank. They made a bad batch that leak oil.