Thank you very much for all the posts, I'm very happy about that!
To answer some of the questions:
I'd mainly use the macro lens outside, and I'm not really a tripod fan to be honest. (Maybe it's because I do not really own a good one - probably should pick one up one day...)
Obviously working distance is not an issue when shooting flowers - I get that.
However, I do really want to get some nice
butterfly photos. I tried that a year or so ago with a 450D and the Sigma 70-300mm - overall it was a pain.
But here's my problem: Either I go for the 100mm which is faster and has IS (I like both things there!) or I go for the 180mm granting me more working distance, however I'd have to deal with slower AF.
Perhaps the 100mm and a 1.4x or even 2x extender would fulfill my needs?
Good thing would be that I could also use that extender on the 70-200mm (which is f/2.8L IS II, to answer another question) which would at least bridge and let me find out if I'm really into bird photography or if I just want to do it because I can not do it at this point.
And if I'm really into it, I'll have to save for a 400mm I guess.
So what's your thought on the extender thing? I know image quality would suffer a bit, but in the end I prefer a picture that suffered a bit to a picture that's not there at all.
And background blur is not the most important thing to me. Since higher background blur does also mean I have to set a higher aperture (number that is, of course the aperture itself has to be decreased) in order to get everything as sharp as I want, it's probably not the best idea. Especially not when the one with the higher background blur has no IS.
Let's see what you guys think about it, I really appreciate every single feedback you guys can give me.
Thanks a lot in advance.