Gabriel Garcia uses Soloists so that's Seymour Duncan JB mostly I think. I can't comment on the Dimebucker so much but I can certainly comment on the JB and Bareknuckle pickups as my current SL3 uses a JB in the bridge and my previous guitar was loaded with Bareknuckles.
Firstly, if you want that searing tone, you want ceramic magnets as they give a far more cutting tone, which is why they are invariably used on mahogany bodied guitars, so they can cut through the dense wood. Having said that, Jackson use them extensively on their Alder bodied guitars and that's what gives them that great cutting tone for Metal music.
The JB is a very good pickup and I have no immediate urge to change it but it's no Bareknuckle. Those Bareknuckle pickups aren't cheap but they are the best you can get and if he wants the best, that's what he should go for. The JB has power but it doesn't have the same quality or depth to the tone and it doesn't have the same articulation as a Bareknuckle. If you're looking at a Bareknuckle pickup, there's two I would suggest you look at. The first is the Painkiller you have in this thread's title. It's a high powered pickup and I have no doubt it will do exactly what you want and better than anything Seymour Duncan have. The other option I'd consider is the Bareknuckle 'Cold Sweat'. Like the Painkiller, it uses a ceramic magnet so it has plenty of bite and articulation but it is less powerful and that translates to a richer tone. They use plain enamel wire on this one, which helps to create a slightly rounder feel to the sound. It's based on the Gibson Dirty Fingers pickup that John Sykes used in his Les Paul when he recorded 'Cold Sweat' with Thin Lizzy but it's a whole lot better. Whichever one he puts in the bridge position, he should put a 'Cold Sweat' in the neck position. It's the most popular neck pickup that Bareknuckle do by some considerable margin and it holds that position for a very good reason.
If in doubt, email Tim at Bareknuckle, detailing exactly what your rig is and what you're looking for and he'll tell you which of his pickups will be best. My advice, having dealt with him before, is do exactly what he says
Get Bareknuckles and don't look back.