so i want to upgrade my old crappy bass ---> new bridge, sand the neck, but i cant decide what kind of pickups. i want to get the most metal pickups possible ( i can get any sound i want with my SR500 anyway) oh yea its a p-bass

Hahaha, that be vauge man... If you want the most classic metal pickups (like AC/DC or metallica) then I suggest passive overwound humbuckers with high output pole peices for that deep thrashy sound. But if you want that new metal sound then you need active pickups for THat deep rich tone. But if you want an extremely metallic tone liek Tom Morellos guitar than that is all in some reverb, short delay, and underwoudn pickups with high attack pole peices! :P
DiMarzio and Seymour Duncan have some high output metal bass pickups (especially Seymour Duncan). But, like it was mentioned before, for that true metal sound, you need an active preamp.