Unless you have diabetes markers, glycemic index is almost entirely irrelevant, it's like people that avoid gluten/lactose who aren't intolerant. Studies that made links to glycemic load to overall health have largely since been found invalid.
Thank you for that link. That study period of 5 weeks is not nearly enough to evaluate high versus low glycemic index diets upon metabolic syndrome. All the study showed was no acute impacts (good to know, but not conclusive enough for prescriptive direction). After finding that out from the study linked to, I tried to find a study that tracked glycemic index in meals of participants over 1-5 years, but couldn't come up with any, so if you know of any to link to, I would really appreciate it.
It's still valuable to know. I am a diabetic, and so are a lot of other people. I would choose lower-sugar chocolate if it were available (I don't eat anything but plain dark chocolate now but I do miss Kit-Kats), but if it were actually worse for my glycemic control than the regular Kit-Kat bar, I'm not doing myself any favors.
example of newer studies: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4370345/