Re: Is there something up with RG520QS's?
Yep, 3120 is just the older brother of the 520.
That said, the 520 is pretty amazing - and plays the same as any MIJ Ibanez.
The 3120 is really nice, it has all the prestige features. In fact, the 3120 is arguably the most famous prestige. The binding effect, the fret details, the fancier top. etc..
The 520 is a little more stripped down. It has v8/v7 pickups, which are not that bad, especially when you do that phantom mod. The DiMarzio's in the 3120 actually seem to be a bit muddy for mahogany. I think there was a version with a Tone-zone bridge and an Air norton in the neck, and a version with the TZ and a PAF pro. The PAF pro is a better fit for mahogany, but the TZ could be too bassy. I just got the pickups on my 520 changed to an AT1 and a FRED in the neck. I will get it back saturday.
The 520 neck isn't all that bad in comparison either. I love the bubinga-striped super-wizard neck. It is just as thin as the original, and actually looks classier with the bubinga stripe. Fret work is average for MIJ Ibanez. Not prestige, but it's fine.
Edge bridge on both, until 2003. I personally do not like the the Edge pro as much as the original edge, but opinions vary. Personally, I like having the locking studs, which the Edge-pro lacks.