100 macro, L or non L?

I think you've made a sensible decision. I have the 100mm L IS, and I love it for its refined way with contrast, its creamy bokeh and its 4 stop IS for distance shots, but for close-ups the IS is really not worth upgrading for. The reviews I've read say you get only around 1 stop from it. If you've got the 100mm non-L, use it! Commit yourself to it! I've got back problems too, and so I use a tripod where I can with remote trigger and manual focus. Very rarely do I get any huge benefit for macro work from the IS.