Sorry but I don't believe the planing claims... 42stone with a 6hp... we could all downsize our motors if that were true.
If it's rated to a 10hp... and you want to go to sea... and you have the budget for a 10hp... then that's the best size.
If the sticker says 9.8/9.9hp then that's what you get... and performance differences between makes is minimal.
If buying new for me the downsides of the 8hp is they are almost always the same motor as the 10hp just down tuned. So they weigh the same and why would you carry that weight about and not have the extra 25% power?
In truth Tohatsu/Mercury/Mariner/Suzuki are very similar prices... it's usually just Honda and Yamaha that can cost more.
Not that I'm pointing you at it as a buy in particular but have you seen my review on the Mariner 9.9 I bought recently?
http://www.rib.net/forum/f36/mariner...tml#post777731
Edit: I see Gilly's post appeared as I was typing mine. If his is the 4-stroke and a few years old then barring the hood shape it will be near identical to mine and save you about £650 off discount prices.... and he's not that far from you.