Unless you want a really dark (high DC) metal sound, PAF's are pretty much the only way to get a decent sound from an all Mahagony LP i think. Compared to an SG a LP model will sound even darker in comparison, so yes the same rule applies IMO.
You cant get a less dark sound by putting more middy pickups in the guitar, a dark sound is about a lack of midrange typical to mahagony. Putting a pickups in such a guitar to compensate that lack wont work because more than nothing is still a very little bit more of nothing.
What one should be looking for is a pleasant high that most surely will 'pull up' an impressively deep and warm(and hopefully tight) low end sound.
And dont underestimate the 50's custom LP sound, yes its dark, but also very emotive, has great acoustic qualities and is probably one of the best rythm guitar sounds imaginable.
So thats my 2cents, i would go for SM's because they would fit the bill perfectly, if you dont want a dark sounding guitar, just play something else...... :roll: