I imagine the sound you heard was like the first few seconds of this vid?
In that bike's case it was the bottom end on the way out and there was play in the conrod but obviously shouldn't be the case with your bike.
Could be compression related though I guess.. Did you get your cylinder checked for correct sized piston?
Might sound silly but you are using a genuine head gasket or an Athena one yes?
It's a Grom with a KTM LC2 engine (Same as DT engine)
A chap named Mike Taylor is building it. Pretty cool I thought. I found riding an actual Grom pretty dull so a DT engine might make it a bit more interesting.
Just to chime something else in, my TDR doesn't really have much past 9-10k either, but it seems to be due to a small hole where my silencer meets the expansion chamber. Whenever I patch it up, I get much more pull up the top of the rev range. Sadly my fixes don't last long 
Would you consider moving the forum to a faster machine altogether? Maybe a VPS?
Vultr.com $2.50 per month for a decent enough Linux server. I'm sure a few of us on here would be happy to donate a few quid to help the cause 
Think most places charge now. Surrey and Horsham do and there's lots of lanes for the opportunists in these areas.
Some lovely looking bikes here! Personal favourite is your friends TDR
