Thanks Francesc, but though you're absolutely right, that's not enough to me. :)

Some people say, 2200 in this case is better than 400 (both zoom-lenses)? Of course i do believe, that a fixed-focal-lenght-lens 400/f4 is a lot better lens then the 70-2002 (at 400mm) .. but sorry, i'd buy a car if i had that much money (starting at 5500 Euro) sigh. To me (as to the most people i think) this is a careful balance between desired quality and available money. Having enough money, i'd say "yep, you're right, let's throw all converters in a nearby river" :-)). But with my limited budget i have to ask, how to get the most out of my money with knowing, that i cannot get the best that's possible.

Therefore, the 70-200 2.8 IS would be great in the range i use a lot with the option to expand it via converter in the rare but sometimes necessary range 200-400. But is it good enough at 400mm compared to the 100-400? On the other hand, the 100-400 is cheaper and offers the whole range i need in one lens .. with questionable handling and less quality in the lower focal lenghts which i do need more often.

As an alternative, i thought about 300 (fixed-focal-lenght)*1,4 which will be way better than 200(zoom)*2, but that leaves me with my less than perfect 75-300 IS or will cost double to buy both. Also, there's that problem with fixed-focal-lenght in handling. If you do know, where the object to shoot will be, fixed-focal-lenghts is better, but as i'm no pro, i like the versatility of a zoom lens (once again knowing, that i do get inferior quality).

Sorry, just wanted to explain what i think, please don't get me wrong Francesc and thanks again!! :)