I thought all RG550's were equipped with Edge trems not Edge III, but I'll leave that to an Ibanez expert to answer.
Super wizard necks on older RG550's and the RG20th are 17mm at 1st fret - 19mm at 12th fret, Prestige necks are 18mm at 1st fret and 20mm at 12th. May not seem like a lot but it's noticeable when you play.
Okay thats good. So i assume the neck on the 550 and J custom will be pretty similar?