I'm familiar with the NPC equipment charts, irdeggman, I'm just wondering how much harder it makes the fight if you give an 8th level NPC's equipment to a 5th level character. Say, for instance, a sorcerer from a noble family who hides his inadequate grasp of the Art by toting around the fruits of his family's finances, or an assassin given just the right item to slay the NPCs when he would otherwise not be able to. And, of course, there's always the opposite direction, as well - what's the CR of a doughty knight who's lost his magical armor and sword, or of a recently-robbed dragon?
Using the 5 gp = 1 XP rule is good, but it gives you strange results over the 20 levels because gp and XP increase at wildly different rates, one more-or-less linear and the other more-or-less geometric. I was considering doing the full chart relating XP to gold and trying to smooth out the curve for an average ratio, something like +3 "gear levels" = +1 overall CR. That would be a lot of work, though, and I was hoping I had missed an obvious shortcut or that someone else had already played around with this idea.
I've seen infrequent examples of this in a few books, but those all seemed to be a matter of just eyeballing it. Which I can do, but the number-crunching side of my DM's soul doesn't want me to do that.