Well my first impressions of the 59/Custom Hybrid were a little off beacause there was a little wiring problem in my strat. At first it sounded pretty bright. Now that I got the wiring issue straightened out, I am enjoying all the glory that is the 59/Custom Hybrid. The first thing I should tell you about the pickup is that it sounds more like the Custom than the 59.
The EQ is rated B6/M8/T8 I think, and that's accurate in my opinion. You get plenty of thunk from the bass if you want it, but the midrange stands out in a very forward way just like the Custom. However, there is an edge to this pickup that the Custom doesn't have and it's that particular edge that you get from Alnico. I'm not sure what to call it but it's something I hear in alnico pickups and speakers that ceramics don't have.
The Custom EQ is rated at B7/M6/T9. I would say that's fairly accurate except it never seemed that bright to me. A treble of 9 would seem to me to be considered a "bright" pickup, but I never got that from a Custom. The 59/Custom hybrid isn't a "bright" pickup, but I think the term "crisp" is a very good description of 59/Custom.
The feel of the 59/Custom is very loose. In that same guitar, a JB is super tight in comparison. Likewise, in terms of how it holds together, the 59/Custom is kind of loose but the bass is tighter than a 59'. The only issue I've found with the 59/Custom is pickup height. It's very sensitive and immediately sounds out every touch of the string, and it has a loose feel so it seems a little harder to control and keep the strings quiet. In that way it's kind of an unforgiving pickup. Too close to the strings and the 59/Custom is too sensitive, but too far away from the strings is kind of weak.
The crispness and straight-forward midrange of the 59/Custom reminds me of a Dimarzio D-Sonic (screws on bridge side). They have a beautiful sparkling quality without being too bright.
Anyway, this pickup replaced a Pearly Gates and seems to have tempered the sizzle a bit. I like it a lot but am not sure if I'll keep it or go back to the warmth and fullness of the PATB-1.
Here's a quick audio sample of the 59/Custom Hybrid with heavy overdrive. Sorry about the mistakes because I was making it up as I played.
Strat with 59/Custom Hybrid and Fender Machete, scooped mids