I would put in an Irish Tour for a nice strat sound. I have Trilogies with my H/S/S Nailbomb set, but I wasn't looking for a real Straty sound, I was looking for more of a Jackson mid range push. I know the standard single coil shipped with the Nailbomb is the Irish Tour. I also think it will go well with the Riff Raff. I have a set of Irish Tours and they shound great.
Depending which coils you are using, you probably will have to get RWRP if you want hum canceling in the combined 2 & 4 setting. Another option, if you really want to hve a Strat sound, is to use the super switch (4 pole 5 way), that Tim sells and wire it for Nailbomb/screw coil NB/Irish Tour/screw coil Riff Raff/Riff Raff. This would give you the classic strat sounds + 2 HB sounds.
Cheers
Phil