Thanks Harry - I think one of those straps would be a good idea whatever the lens attached - much more comfortable than the Canon one i should imagine.
Photozone review of the 70-300
http://www.photozone.de/8Reviews/len...56is/index.htm
Build quality is not, I imagine, anywhere near as good as the sigma and certainly at the budget end of the Canon range. I would'nt envisage using it with a tcon - far too slow. It's all a matter of compromise and, after using my 28-135 IS today in grey drizzly weather, the thought of IS does seem appealing.