Any more comments or updates about your 20700 bored C8 tube? IMO this is the best way to utilize the increased performance capabilities of these 20700 cells. I assume you used a boring bar tool on the lathe? Any difficulties with the tube being too thin or anything?
I’m thinking about making a quad dedomed XPG2 C8 light and using a 20700 cell. Four ~17mm TIRs (like used in a S2+) should just fit in the C8. This setup should make about 3000 lumens and 90 Kcd in a nice compact light.