I did the rebuild myself, so nobody else to blame. The top end kit was from Cooksey, so I don't think he would have steered me wrong with the piston suggestion.
I didn't measure the out of round because I had the cylinder replated by powerseal before the rebuild... which sucks even more in retrospect.
Piston rings were the right way up. C-clips were in the piston, and I don't specifically remember and odd noises before the end.
Gas and oil were mixed.
Con rod has 0 vertical play but probably 1.5mm of horizontal movement.
The failure occurred a when I was at 1/2 throttle riding around Vermont a few days after I raced in a hillclimb event (street, not dirt). On my last run, I had a bit of a crash and laid the bike down. It wasn't fast or a terribly hard hit and didn't seem to have any issues for the next couple days.
Break in was done with a few heat cycles and some midrange revs. I know there are many views on which way is correct, but that's the one I ended up going with.
Jetting seemed to be on point, if anything it was a little rich. The previous top end that was in the bike when I purchased it lasted for a year and lots of abuse.
2 things did occur to me:
1. There is/was a slight exhaust leak by the powervalve
2. Completely forgot to mention: I installed aftermarket radiator hoses after the hill climb, maybe something happened with water pump or thermostat?
I found this picture from before I installed the new rad hoses.
This is what the cyl/piston looked like after the hillclimb and like 2 hours before it went boom..
Thanks again for the help guys