I'm sure the OP is capable of controlling his urges to see what happens if full travel inputs are applied at Vne. Give the guy a little credit for not being an idiot with a death wish.
As for the 'envelope' the UK does not have an Experimental category. Permit to fly aircraft are not Experimental and their airworthiness is closely controlled by the LAA. Granted, the Turbi is a very old design, but it is well known to the LAA as are its limitations. I'm not suggesting LAA oversight is equivalent to certified aircraft standards, but its not the free for all that many other countries enjoy either.
I'm sure that the OP won't be exploring that envelope without knowing what the design limitations are and whether the LAA have changed them in light of information from the fifty odd years these planes have been flying. There's nothing wrong with exploring envelopes if you know where the boundaries are, so please stop acting like 'exploring the envelope' is a simile for aerobatics, because it is not.