I am looking to make a much needed upgraded to the 70mm+ range of my lenses. I know this is a topic that crops up quite frequently and the answer is always, quite rightly, buy the 2.8L IS II. Unfortunately my budget cannot stretch that far and is capped at £1000 which puts the Canon f4 L, Canon f4 L IS, Canon f2.8 L USM non-IS and Sigma 70-200mm f2.8 EX DG OS HSM in the frame.
My work is split 50/50 between studio portraiture and concert photography. Really it has to be one of the f2.8 lenses. The concert photography is a mix of relatively stationary singers and more active bands or cabaret performers where IS wouldn't really help. The studio work is often tripod mounted but I like the freedom to hand-hold where possible.
As I might benefit from IS I am tempted by the Sigma but most reviews raise concerns about corner softness, particularly with the lens wide open. Equally as the Canon f2.8 USM is an old lens there aren't many current reviews that go into the same detail so I'm unsure whether it fares any better.
Any advice from those with more experience with either lens would be greatly appreciated.
Many thanks in advance.