Hey guys, I am shooting on a canon 70D which i absolutely love love love! I am living in China, but i have been offered a chance to go to South Africa to work as a research assistant on a wildlife reserve. I have been wanting to get a 70-200 for a while now, i always wanted the canon 70-200 f2.8 IS but alas my little plastic friend cannot stretch quite that far. So my choices are between the Sigma equivilent; 70-200mm f2.8 OS or the Canon 70-200mm f4 IS. I would really like to know your opinions on what you think would be best. I like to shoot a bit of everything really, and i like to shoot outdoors at any time (this probably isn't helping you guys much hehe), so i guess versatility is good. But i also do a lot of walking, and this is where the f4 i guess would be good as it will be lighter. If i do decide to go out to africa then i will be doing a lot of wildlife photography which is something i really want to do more of anyway. Living in China the price ranges of the two lenses are very similar, so thats not really too much of an issue. Both lenses range from between £300-£600 depending on where and whether i buy new or 2nd. I am going home for Christmas soon and my brother has the canon, so i shall be playing with that for a while to see if that helps my decision. Any opinions are greatly appreciated.