PS Audio Amp tube rolling

Its time to replace my PS Audio BHK 300 monoblock's tubes. Does changing tubes from what were the factory set to another brand of tubes have as much difference as changing tubes in say a PS audio BHK Preamp. I changed/upgraded tubes in my BHK preamp and it made a fantastic difference.  Will the same hold true for the mono amps (more, less, same). If you have done this "rolling" in the mono's what tubes worked for you and what differences did you hear.