Not sure of a technical answer, but one thing to consider is the replacement costs for the pads that you will consume. I get about two track days out of my pads (Hawk DTC-60), so it adds up fast if you do a lot of track days. Similarly, at some point you might want to consider using 17" wheels on track because tires in that size are less expensive than 18". A 355 won't fit in most (any?) 17" wheels. 345 may not fit either.
I am at the limit of tire adhesion with my 330 4 pot Brembos. No problem with brake fade. Anything bigger would not improve performance.