Re: ibanez rg370 vs esp ltd m100fm
1. No idea.
2. The difference in a DX model is usually a few cosmetic details... Sharktooth inlays as opposed to dots. Binding on the neck. That sort of thing.
3. There are bad Floyds and there are great Floyds. If you're buying a newer 370, you'll get either an Edge Pro II or an Edge III - both are fine.
4. Generally the first two digits will give this away. For most (all?) of the lower end Ibanez line, 2005 models received an upgrade from Powersound to Infinity pickups. An improvement. These models were all upgraded a couple years ago to Edge Pro II bridges from the crappy LoTRS II. Also, I believe all the 2005 models now have a 3 piece Wizard II neck with no scarf joint.