For my size/build (6'4", most of my life spent at 260 or more (happily down to 235 now)), I have always been flexible to an extent others would comment... though not with the contortions described in the OP. At that size, I could put my foot behind my head and from into a leg-front split without much difficulty - the trade-off being that my joints are loose (and slightly malformed, deficient grooves) in general, and I have damaged both knees and one shoulder significantly as a result.
M.
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My thanks to all the wonderful members here; I will miss the opportunity to continue to learn and work with you.
For those who seek an alternative, it is coming.
So long, and thanks for all the fish!