Thanks Bladerunner - that matches what I experienced whilst you were away in Ireland. I asked Cotswold Motorrad how much to swap my June 2010, 12k mileage GSA against a fully ferkled GT and the answer was £9k! Considering I paid £13.5 for it, that's pants, so looks like a "conversion" isn't too likely in the short term.
Didn't want one anyway, so there...