If you insist on riffing with the neck pickup... then logic says that you need the Painkiller Neck.
why?
because it is the only Ceramic Neck humbucker of the high output category that BK offer. So in theory it would be very TIGHT and focused.
but your best bet ALWAYS is to talk with Tim.
Just tell him what kind of guitar it will be in (woods), that you want to use the neck pickup for your riffing and give him some band examples.
It would also help if you give him some details of the sound you like:
1) focused, tight, loose, versatil
2) trebly, midless, alot of high mids, low mids, low end
3) articulate, saturated, cleans up well, compressed, don't care about cleans
or you can also try the "sound clip" or "read alot of threads" methods.