Liking the Concorde idea Martin @ EGLK
IO540 - you got a better response than me; they didn't even bother responding to my query a few months ago! Although I do notice that they claim that it would be the only 4-seater aerobatic aircraft on the market was slightly inaccuarate - what about the Yak-18? A retro-active poor man's Grob 140 TP prehaps?
(although I may well have mis-read it, - I'm almost certain that it's the only 4-seat turboprop GA aero-capable aircraft)