Re: Deciding for my SG
For G'n'R (if you want a more convincing Slash tone) you'll want Alnico II magnets (Alnico II Pro, Custom Custom) When Metallica used Duncans (MOP and earlier, I believe) James used an Invader and Kirk used a Distortion.
Between the SH-4 and the SH-5, I would choose the Custom, as I have heard that JB's can get a little thin in SG's, but that is not from personal experience. Also, what amp, effects, etc are you using?