Having flown both the 600Hp & the 675HP models, (both on Wipline amphib floats) definately be looking for the 675HP model. It does make a huge difference. If you can find one with single point refuelling, that makes life a lot easier too, nothing like climbing up on top of a wing when it's wet trying to haul a can of Jet fuel or a fuelling hose (wear your swimmers because that's where you are likely to end up).
I think you will be hard pressed to find one on straight floats, amphib floats are far more popular (and practical).