--the literature at Iherb, in an attempt to summarize the meager amount of literature on the subject, seems to indicate that the ratio of effectiveness for alpha-lipoic to R-lipoic is in the neighborhood of 5:1 to 10:1.

When I switched from the former to the latter, I went from 600mg/day alpha lipoic, taken in two 300mg/day doses (with meals), to 100mg/day R-lipoic (wtih breakfast). I don't think I've noticed any change in effectiveness--of course, it's hard to say just how effective these are individually, given all the supplements I take. Since lipoic has considerable blood sugar reducing properties along with its antioxidant ones, I use the results of the glucose tolerance testing I do on a regular basis as a rough guide.

One thing I do appreciate is the reduction in acidity achieved by taking one 100mg/day capsule (although I've noticed different brands of R-lipoic vary in this regard considerably for me).