Chip; it's not boost as such, but high cylinder pressures together with high revs causing nose flex. There are NA race engines revving to 8500rpm with no recorded fauilures. As you say though, the hard part is finding out exactly for sure what happened, hence nylon bush test for a start.

Will; it's interesting stuff for sure and great to see someone test the theories.

Although Lee has found something else very interesting when taking the engine apart

Anyone who has or knows of an oil pump failure: can you confirm what size gudgeon pins you were using?