Good news for all!
Having just popped into Coopers to see the new tank bag, the parts person told me that there was no new small tank bag for the GS12?

'No definately not on the system', as he sat looking at his screen! A bit embarassing for him as directly behind him sat on the shelf were both new versions.
I offered both versions up to the bike and decided upon the new small version, as I don't personally like large bags on the tank, and found the bigger version does tend to sit quite a way back on the tank, I prefer sitting forward. So the small one was my choice, great fit, quality and no need to use the old velcro system!
I had an SW Motoech engage bag on my old model, and really rated it, but as the fitting system has changed on the new bikes I sold it to a mate for his 06model. But SW Motech have now just released a new mount for the 08 bikes, but the mounting horseshoe clip, without electrics, costs £45 before buying a bag
So on balance I decided for the small BM one at £85. For the GSA owners I saw an article on Advrider site showing how to modify the new lower mounting bracket of these new bags so that it can be fitted to the GSA model (without needing to use the velcro pad thingy).
So good news for all then - two types of bags that are good quality, work and fit really well. Can be fitted to both models (with a little modification) and SW Motoech's bags can now be fitted to the new 08 bikes.
Pay yor money and take your choice!