This is good but I think you could have snuck some qualitative analysis in there as well. I'd be interested in seeing the variance in performance quality. In each tour or year or era, how long would it take before I heard a top notch version? It would be interesting to see that taken to a set or entire show level as well. Granted, most fans probably already have well established ideas on this, but a visual representation like you have done here, would be interesting. You can really get crazy with BI and you could probably spark some debate for the right topic. Kudos for the time you've put into this!