So I got the chance to play with my professor's 70-200mm f/2.8 EX macro lens today, and have to admit I'm in love. I have been looking and researching for a long while now into a long telephoto of some variety, and was curious about getting your thoughts on this idea. My thought was to start with this lens. The lens as it is is a quite useful length, and the LL capacity of f2.8 would certainly be a nice thing to have trying to photograph moths at night(which is one of my new favorite things to do I have to admit). The problem with this lens is, it's shorter than what I wanted (I was looking for ~400mm). However, with a good quality 2X tele-converter, I'll have the zoom I wanted, and keep it at about F5.6. I realize sigma has a nice 80-400in F4-6.3 for right around 1000$US, But I feel like this combination would offer me the best combination of a high quality, low light zoom lens, and the longer zoom when using the tele-converter with a similar(if not slightly better) F-stop than the single large lens, and would weigh less(I have also used the large 400 and 500 models.....there heavy as hell), while remaining within 100$ of each other. In short I think it would be a better investment into a sort of "do all" setup that would leave me happy, and would allow me to focus on a better prime macro lens, and acquiring a higher quality wide angle. This is important, I'm not on an unlimited budget, and intend to invest in a high quality setup that will let me do what I want without having to beg and borrow to get it done. My main purpose in wanting the longer zoom in and AF lens is photographing birds in flight, and other general wildlife photography. Opinions?