Thanks for the thoughts, I'll order the Canon and Sigma 1.4 lenses and try them both out and decide which one to return once I've had the chance to play with them both to se if I'm happy with the results.
I bet the retailers must love you.
Could you not try them in a high street shop or if you're intending to use one for say a whole weekend then really you should hire them. Isn't really too cool to do what you're proposing - you'll either screw over an honest retailer or screw over an unsuspecting customer of a dodgy retailer who's happy to re-sell your return as 'new'.