Mariner 6hp

[samt]

I have just bought a Mariner 6hp (yr 2000). It is the 2 stroke twin cylinder model (210cc). I have been looking at the other 2 stroke mariners and it looks very similar to the 8hp and maybe the 9.9hp. Can anyone confirm this. Will this affect performance (Power to weight ratio)? What are the advantages to having a larger cc and the engine restricted to 6hp? What speed should I expect on a 3m SIB airdeck?

P.S. I paid £399, was this a good price?