Re: SSL-5 vs Little 59 vs Pro Track
There's no right or wrong answer. I have SSL-5s and Little 59's and IMO they sound a lot a like, which is to say, think and dark. I prefer the sound of Little 59's split or parallel to the SSL-5's tapped. I'd go with the SSL-5 (or maybe the YJM Fury) in the bridge to maintain a stock look while getting that more versatile bridge output. The Little '59 will look more obviously different than the SSL-1s.
I haven't used the Pro Track before, but from what I understand it also targets a PAF tone so it's probably in the same ball park as the Little '59.