Yep, Texas Specials will get you the SRV and Los Lonely Boys vibe. They do the overwound single coil pups and heavy string guage thing so upping the string gauge will help get that explosive single coil sound. I read somewhere that the Los Lonely Boys guitar player puts .11's and Texas Specials on all his guitars.
Not sure about John Mayer, but going by the "v" shape EQ of the pickups in his Fender signature, the Alnico will be the better choice. You won't exactly get the classic brilliant strat sound from the Texas Specials.