I rented the Canon 100/2.8 L IS and did a test for my purposes. IS is supposed to be limited when near 1:1, for me it did not work at all. Was able to hand-hold at 1/100th and faster, as I already do with my NIkkor 105/2.8.
It is very sharp, a bit bulky compared to the Nikkor (USM motor and IS gerbils). Not that big an improvement over the Nikkor, so I'll pass.
Here are my test samples (this is not a formal test. It's a test for the way I shoot, hand-held, natural light, using my very own one-of-a-kind
body to hold the camera even!):
I may rent the Zeiss 100/2 or 50/2 next. Wish I could find a Voigtlander 125/2.
There's a few more images on my blog:http://markcolman.tv/?p=758