I guess you should look at the Sultans, the Pat Pend 63 and the Mother's Milk. The alnico II-magnets of the Sultans provide a softer response in the bass and treble then the other two with the alnico V-magnets. They all have, one a bit more then the other, a scooped midrange. A baseplate will add some extra body to the bridgepickup. I would get one.
(Btw, John Mayer's sound is not only a matter of pickups, the quality of the tonewoods, the thickness of the neck and the used amps play a role in that).