?Does anybody know the performance of this lens? (can it be compared to a 70-200 f2.8 sigma or better?)...or a good site who make serious photographic equipments tests???

I have this lens and enjoy it very much. I usually use it with a Sigma 1.4 which brings down IQ somewhat but even with it, IQ is on a very high level. I've used the 70-200 f2.8L IS only once (rented it for a wedding). The results were comparable for those photos. I didn't get a chance to test it out on the type of photos I normally use the 100-300 for.

Both are well built. Very heavy and solid. Both have IF which is good. I really hate lenses that extend when you zoom. I prefer the longer reach of the 100-300 (actually I'd like even more reach) but the 70-200's IS is something I would very much like to have. Right now I pretty much only use the 100-300 with a tripod or monopod. Midday I could hand hold it quite easily but I'm not usually after fast twitching animals so a tripod or monopod suites me just fine.

For good reviews of lenses go here.

Thank you very much for the link and information. I was about to think that nobody in the world was having this lens. I worked a year and half in a big photographic store and I never see one sold, even if I was finding it very interesting. Maybe the price is a little too high? However you answered most of my question, hope I can buy one a day!