Thanks toor. I shall have a look through those.
My first walkabout was the Siggy 24-70mm f/2.8 EX DG, which is built like a tank (and probably weighed as much). It was slow to focus and had a tendency to flare even at the thought of Sun. The 70-200 2.8 is a very different beast, the HSM AF motor is fairly nippy (and quiet) and optical quality is pretty uniform. I have no issue with 3rd party glass (I picked up a Tokie recently which I'm very pleased with), but they can be hit and miss.
I'd suggest reading reviews from reputable sites like the ones toor posted. But there's really no substitute for going to a high street vendor and putting the lens on your own body to get a feel and put it through it's paces.
Good luck!