If it helps at all I'm very jealous!!
On a serious note having driven both Valiants and Tornados around the 6m mark, I'll put my neck on the line and say that IMHO the Tornado is a much better boat. I have owned a valiant (so am not biased!!) and found it to be a great boat, its just that the Tornados are so much better.
Have you spoken to Laurence Lock at Barnet Marine (www.ribs.co.uk
) as he may be able to put you into contact with other operators of 8.5m Tornados and he is very helpful.
The extra metre will make a big difference no matter what and with the Tornado being hand built rather than mass produced you can get a truly custom boat. I personally like the idea of the transom bracket which lengthens the boat by 1.5m and also gives you extra room inside the boat.
Will be an awesome boat!!