Piston to bore clearance is quite 'critical' IMHO, though I well recall (many years ago!) Malcolm Anderson struggling to start his Group Four bike, yet it won races with a seven thou' gap. I think I am correct in saying that he was so busy @ MSC, that there was simply no time to strip that engine between events to correct the issue.
As for the issue of ring gap, my experience is that a larger gap than the various recommendations is not so critical, particuarly in the case of OEM port widths & two or three ring pistons.
However, larger port widths &/or an increase in the number of ports, inevitably exasperate wear, as does the lack of filtered carburation & higher engine speeds & the ring(s) material.
My advice is that with any modified engine, you need to keep an eye on the ring gap, because although I doubt it leads to power loss, in the two stroke engine, there are other consequences to consider. The obvious, infamous Honda piston conversion had problems with the ring peg material, & any tendency for the ring gap to increase would allow the brass pegs to wear out completely, causing the wreckage of the top end.
(I hope that is a helpful, diplomatic, input to this debate & is certainly intended as a good natured observation
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