In reply to What Goes Up:
Thanks for the replies...
Must admit I hadn't thought about the old non-IS model, I imagined that up at the 300 end that the image stabilising would be important to have, though i have read reviews in the past that compare lenses of the same size, same make, that are available in IS and non-IS models, where the conclusion is that the non-IS is sharper. the Tamron f2.8 17-50 i have is the non IS (or VC as they call it) version, and is reckoned to be sharper than the VC model, i figured at that shortish focal length it was less important to have than on something like a 70-300 tele-zoom.
I may be able to have a go with a friend's old non-IS 70-300 and see what the results are like.