Re: 59 and a C5
That is a good set - I happily used it in my SG for a long while, though a word of warning: the 59 neck can get kind of boomy, especially under a lot of gain. I swapped mine out eventually for a Jazz model and was thrilled with the results. The Jazz has (IMO) a much more contemporary tone and retains a lot more clarity especially when you're got a bunch of distortion going on. The C5 is great for me, as I go from blues to vintage rock to metal, but if you're a straight-up metal kind of guy, you might go with the Custom, as it's a little fatter, fuller tone. As the SD site says, the C5 is like a hopped up PAF - kind of a vintage-on-steroids tone. The Custom is somewhat similar, and has a similar output, but with a more "metal" voicing (to my ears anyway).
To more thoroughly answer your question about the C5, it has plenty of lows, low-mids and highs, but doesn't have a whole lot in the way of high-mids (which contributes its not-so-fat sound).