If you like the XL500 the Miracle Man will blow your socks off! It has more of everything and dynamics as well.
High gain is obviously your aim judging by the 3 p/ups you mention so from the current BKP stable you've got
Nailbomb-hot and organic, good mids and splits down well/cleans up well.
Miracle Man- great tight bass response, smooth mids and screaming highs, pinchs harmonics on it's own!
Warpig-super saturation on the gain front, easily match a 81, also has a great clean tone too.
The Holydiver is a nice pickup but very clean and clear-not enough beef for what you're after.
Add ons-personally, and I'm speaking for myself here, less is more. Whatever extra you put between pickup and amp is going to suck a little signal and load back the pickup. At the end of the day you'll have to see if you actually need anymore..............if not I wouldn't add on just for the sake of it. PDT_015