It's a little late but I thought I should write here my little choice.
After months of work I had the opportunity to save enough to buy the new lens. I have chosen the 150-500 mm from Sigma and strangely it works very well.
The quality of the canon is indeed better, but I like the extra 100mm for shooting animals and I'm waiting for the next full moon to get a nice shot there to.
The following 3 shots were taken with the lens at f/8.0. If you click on the pictures you'll get to my gallery and you can see the entire meta data under shooting condition.
To be precise, these aren't the results directly from the camera, but, I think it's nice to see what kind of result you can get after the postproduction which was done entirely in lightroom.