It's been a minute since I posted this but I finally got it and installed it.
I went from the stock Probucker 3 to a Custom to a Custom Custom. Here's my best take on each:
PB 3: Has a bit of a soft feeling to it, but not muddy or undefined. Good for blues / rock but not so much metal. The upper mids have a nastiness, but not in a fun way, which was my main issue.
Custom: Higher powered, more scooped, tight low end. Sounds great for what it's meant for, but kind of lacking in that little something I want.
Custom custom: Perfection! It adds the mids back that the Custom is lacking without really feeling like I'm loosing anything. It sings clearer and has a warmth to it, but the bottom end still chugs just fine. I love the attack on it. It's pronounced without feeling brittle. I can do super fast, tight runs and still hear every note.