Thanks for the quick response JMo (and Ricky)

The Sirac's did the same as you describe at the front, very heavily feathered/scalloped and alternatly worn block tread. That was a large part of why I replaced them before I'd worn all the tread down as being my first bike/set of tyres I had no way on knowing if any problems I was getting was caused by that or something else.
Also good to know the rear is predictable, again like the siracs and BT45's that are nearly worn at the reare. Seems to me that with a narrow width on the rear tyre that they never get really unfomfortably square with any tyre make or model?

I think I'm going to stick with my origional plan and try the tourances when I can (not sure whether to just use another bt45 rear until the front is worn or try the tourance with the bt45 front) as I don't think the TCK's will last long enough to be economical enough.

That said it could be that the much reduced life on the BT45 compared to the Sirac is down to me being more confident on the bike so just being harder on the throttle and tyres...although the Sirac does have a LOT more tread to wear down than the BT45.