Candian L, he didnt say the Pitts was unresponsive - the comment refers to the effort by the pilots behalf when executing the aircraft. Aerobatic pilots from a Pits, CAP etc background tend to go "bang" on the stick to roll, "bang" on the stick to recover, "bang" on the stick to go up etc etc WHEN doing a routine. P51's and Spits do not take kindly to that type of handling. Of course a Aerobat chap can adapt, we had a UK champion who flew brillantly but he had an extensive briefing and had it drummed into him that this was an historic aircraft and the controls are sensitive, speeds much higher etc but your not doing 8g routines.