I have been getting more and more into the wildlife stuff, like the range that this lens potentially offers, I have a 70-300 IS lens which is nice and sharp and pretty fast focusing, but sometimes a wee bit extra reach would be nice and a very fast 200 2.8 and a not so fast 135 2.8, so I would probably pare my kit down to accomadate this lens (probably keeping the 200 2.8) I'm just trying to decide if its better to get a big cover all zoom and lose the brightness (also how is focussing speed? have you tried tracking af?) or stick with what I've got and maybe get a canon 2x for the 200...