Re: How do you match a pair of up's for a guitar?
The neck and bridge positions are radically difefrent, due to the amount of string vibration and energy. The neck is loud, dark, and bassy; the bridge is bright, sharp, and weak. There's no reason to feel obligated to use the same magnet in both. For example: A8's are great bridge magnets, but are usually too dark and powerful for the neck; A3's are ideal for adding neck treble and clarity, but are usually considered too weak for the bridge slot. Manufacturers pair up certain PU's as a marketing thing, but most of us match up PU's ourselves most of the time.
Start with your genres of music, that narrows down your choices. If you play blues and classic rock, a real hot PU with a ceramic magnet usually is a poor choice, great for metal though. If you pile on distortion and effects, you probably want a PU that won't 'mud out.' If you play genres where good cleans are important, and OD is in moderation, you want alnico magnets for calrity and tone color.
When it comes to PAF's just about two work well together, as did the original 1950's PAF's, which had a variety of magnets in them, and weren't calbrated for neck or bridge.
One of the most popular user pairs here is a C8 and a '59N; works well in many woods, for many genres.
In mahognay, a CC (SH-11) is often too dark (A2 magnet). A C8 or C5 are better choices. Because these are 14K, they'll split well (you still have 7K split). I'd recommend having the slug coil active when you split, for a bit more output and warmth (the screw coil is brighter and thinner).
Any high quality PAF in the neck is good, like a '59, PG, or Seth. An HB-sized P-90 works very well with a bridge HB. I've done that in an SG and 335. Gibson does it in an LP or two.
I'm the king of Phat Cats around here (I have 9). Most of my guitars are mahogany or semi-hollow, and the stock A2 mags are way too dark in the neck. At the same time, the A2's make the bridge PC weak and thin. I solved these issues by swapping mags (took out all the A2's) and significantly improving the tones. BTW, I usually mix different mags (P-90's each have two), which is something PU makers rarely do, but it gives you many more tone options.