I already saw several matches from Gunter and he does NOT have a P-Yamazaki or Rugal at this level. P-Rugal is really one of the best P-players around :)
Been said P groove is the strongest groove in the game since 2001. IF you can parry a high level....its childs play. Even rc gets parried. Everything thats considered strong can be parried....then that shit aint nothing. Sagat crouching fierce aint shit if i parry it...cross ups aint shit rc aint shit tiger uppercut aint shit...get all dat shit outta here!
Personally I think A groove is probably the best, sure P groove has awesome potential (and is my favoriiiiiite) but custom combos are busted as fuck in any context. Especially with meta teams in this game.