Thanks for all the nice responses - sorry about the dura ace but in the end I decided to go for the known and tested because i didn't want to change the set up on what will now be my winter bike.
Not sure of the size - it all got a bit technical because of the slightly sloping geometry and I somewhat lost the plot along the way - but Rohan at Cycledauphin has the info.
It being a very sunny and dry day i had half an hour on it this afternoon - too early to say but I couldn't fault it so far - I guess summer may come early this year!
Thanks for all the early input and ideas - the owner of the shop, Dave Flemming, delivered it personally which was a nice touch.
Alan