Sorry, I did not read the whole thread so I don't know what others have said.
But I do have a 7D with the 100 mm macro (old one) and the 500D for my 70-200 F4 IS.
I find that I do not use the 500D/70-200 combo very much because frankly, it is a pain to use. I mostly shoot insects and spiders and with the combo you cannot stalk your prey with the camera at your eye because you don't have a sharp image until you are within 50 cm distance (the focal distance of the 500D). So you have to replace your view (move your head) well into the flight distance of most insects.
Most of the time, the movement will scare away your subject.
With a macro lens, you keep the camera at your eye using the focussing ring or autofocus to keep your prey focussed. When the image of your subject reaches the right size (or you dare not come any closer) you expose your shot.
This works much, much better!
I would allways go for the macro. The image stabilization of the newer lens seems a real bonus to me. Maybe just not enough to loose much money over in handing in my "old" 100 mm macro.