Look here. It's not a complete list, but you get the picture...
RG8xxx - Japan, J custom, Dimarzio pickups, hand crafted
RG3xxx - Japan, Prestige, Dimarzio-made IBZ pickups, maple top
RG2xxx - Japan, Prestige, Dimarzio-made IBZ pickups
RG1xxx - Japan, Prestige, V-series pickups
RG7xx - Japan, Wizard neck, later models had direct-mounted pickups, early ones did not
RG6xx - Japan -- similar to the RG7xx series, but only intended for Europe
RG5xx - Japan, Wizard neck, Edge Pro
RG4xx - Japan, Wizard II neck, Edge Pro (early RG470 had Wizard neck and Edge trem, then production moved to Korea and the spec suffered)
RG3xx - Indonesia (was Korea), wizard II neck, Egde III (was Edge Pro II)
RG2xx - Indonesia (was Korea), Wizard II neck, non-locking trem
RG1xx - Indonesia (was Korea), Wizard II neck, pickguard, non-locking trem
RGx7x - H-S-H pickup configuration, direct-mounted pickups, sharktooth inlay
RGx5x - H-S-H, pickguard
RGx2x - H-H, direct-mounted pickups
RGxx7 - 7-string
RGxx1 - hardtail
RG2550 = RG2xxx + 5xx + x5x
RG2550 = Japan, Prestige, Dimarzio-made IBZ pickups, Prestige Wizard neck, H-S-H, pickguard
RG370 = Indonesia (was Korea), Wizard II neck, H-S-H, sharktooth inlay, Edge III
RG321 = Indonesia (was Korea) , Wizard II neck, H-H, hardtail
RG1527 = Japan, prestige, V-series pickups, Wizard neck, Edge Pro, H-H, direct-mounted pickups, 7-string
I definitely like the bound neck over the unbound RG5xx necks, and the 770DX could be considered only one step down from a Jem777. IMO, they were a step above the RG5xx guitars, others might feel differently.
I agree. My RG750 neck was amazing when I first got it. It's well worn after 17 years of hard playing, but it still feels awesome now.