I have a Ribtec 6.5m. It is a 1997 boat and the build of the hull is excellent. The deep V carries on all the way to the stern and gives a nice ride in rough water.
. With the 200 Mariner on the back I have had 47 knots, but need to change the prop to a larger pitch. When fully loaded with 6 divers and twinsets (very heavy load) I have pulled 35 knots. Its sea keeping is excellent and handles large seas with ease. It can be a bit rocky at rest as the tubes are well out of the water but the ride more than makes up for it.
EDIT: Should you ever come down to Devon and want to try one let me know and I'll take you out for a spin