The solent 6.5 and a 150 optimax seem to be a good match...
http://www.rib.net/forum/showthread.php?t=20592
They will hit 40 knots easily... I think they top out about 45knots. A couple of years ago I went to littlehampton with Bruce Hawsker (spelling?) and his boat seemed to handle nicely in the rough weather...
I'm sure there are plenty of others to choose from, but value for money, a solent is near the top of the list.