@Babbediboopi Well, your 'evidence' is technically just more data. Odd looking data, to be sure, but not true EVIDENCE of any kind of cheat. What I would like to know is his ratio of non-headshots mixed in with his headshots, but as far as I am aware the server doesn't track this in any format it lets the players see.
To be honest, that many headshots per kill would seem to indicate to ME that he just has good aim and isn't cheating. Why, do you ask? Well, how many headshots do you need to kill someone? Initially I had though most guns did over 20 dmg per headshot, but it does appear a FEW have slightly under that and might take closer to 12 hits to drop you with 100% headshots. (This is assuming 200 hps on the enemy required to drop them.)
So you start to take into account the fact that not 100% of the people he fights have 200 hps and thus will take fewer headshots to drop, and surely he doesn't find/use an R99 every match, so often his headshots will do more damage and drop people faster, and I would think we can safely say you can drop most people in under 6 headshots on average. The fact that he has 6 headshots per kill doesn't mean that EVERYONE he ran into he dropped with 6 headshots. I'd like to know how many non-headshots he landed and how many people he landed a headshot or two on but did NOT kill. Those numbers would add much more data to the data you've brought to the table and might make this more 'evidence' rather than just an odd data pattern as it exists now.