i recently got 6.7 in my 5th gen with the jdm h22a engine with the m2a4 box and a blowing exhaust at the flexi with a launch at around 4.5k rpm standard p5m ecu with no launch control

only mods
k&n pannel filter
air con pump & resonator removed
back box
hence me wanting to go the p28 route, with the h22a chip, with launch control on it, extended limit to 8200 and to fix up my exhaust & decat. i was expecting to be close to 6 flat until i saw that 4th gen. then it all changed