Hi Leatherhead,
I was in a similar situation my self, i raced Supermoto since it's conception in england until 2005 when i gave up due to family life, also had a WR426 for green lanes and enduro as well as various sports bike. started trials again recently after 20years off a trials bike. I purchased a beta 250 (2008) and have since ridden a few club trials at Worthing (www.worthingtrialsclub.com) and Horsaham both well run clubs with friendly folk who are happy to help. I would strongly recommend the Beta they tend to be the lest problomatic of the bikes along with Scorpa, i am 6,5" and have no problems fitting on it although its all down to personal prefernace. I will be at Hook Woods tomorrow for some practice, you are welcome to come and have a quick go on the Beta as see what you think, my mate will be there on a scorpa and i am sure he will also oblidge.
Cheers
Danny