Re: Bill and Becky L-500XL question
It's different because, when you flip it, the angle at which the pickups hits the strings is changed. It's almost like lowering a pickup or raising a pickup -- that is, when you raise a pickup, it sounds hotter, whereas when you lower it, it sounds fatter.
A word about Dimebag's pickups: During his early Dean days, he probably used DiMarzio Super Distortions, since that's what came stock on Deans back then. By the time he recorded CFH, he was using original Bill Lawrence (Before the merge with BLUSA) chrome-housed L500L's in his guitars, wired up 500K pots and with no tone control. Sometime after this, he switched to BLUSA pickups, playing L500XL's, which he bought from Stew Mac; these pickups did not have the chrome housing. By the time he got his deal with Washburn, he was using L500XL's with no chrome housing. Seeking an even higher output pickup, he modified his L500XL and called it the "XXL". Enter Seymour Duncan.
Only Dime knows exactly what he used, at any given time period. My rough summary is about as close as anyone will get.