Despite everything I#ve told my ladies over the years yep size does make a difference if you can accomadate the 6.5 then do it.
We use an xs 5.5 with a 4 stroke Merc 100 for training on and Its fine albeit a little arse heavy but quite frugal
There is a guy in our yard who has an XS 650 boat is a good un its got a Suzi 140 and he loves it, dark blue toobs and orange GRP looks great, surprisingly. it is called excess
I think however you shoul seriously consider an Opti or Etec 150 the performance will be stunning and both engines are as economic as 4 strokes but boy can they turn it on when they want to. Whe you are buying a new engine the warranty period has to be a big part of your decision. Mercs have 3 years how long do the Suzi#s have.
I really do think hardy#s are fine boats BTW