the standard afm just wouldnt flow enough air to make more power. so it will just stop making power, it shouldnt lean out

probably wont gain any power going a larger turbo on the same boost, as the t25 should have still been efficient at 7psi

common afm to use is a 300zx one, slightly larger than an rb25 one i think. then you will needto get the ecu tuned to suit