I just skim read this thread so apologies if i've missed them, and i'm sure they've been mentioned, but put a set of fuel injectors on that list

For what its worth, i'm running 22psi held with Siemens 55s on my RS500 (standard engine) and I did that with Stu driving and me mapping - it's a really nice drive. Obviously the T4 is somewhat 'dead' below 4000rpm but the punch of power delivery puts a grin on your face!