Re: Rg 550 vs, RG 770dx
i'm prepared to be corrected, but i believe the differences between a 550 and a 770 of the same era will be mostly cosmetic... bound neck, inlays...
i think the 550 will have ibanez pickups as opposed to the made-for-ibanez dimarzios of the 770, but as you say you'll change these anyway that's no big deal.
550 is pickguard mounted pickups, whereas the 770 (while it does have a pickguard) has it's pickups mounted to the body.
there may be some degree of superior finishing on a 770, but after all these years i'd reckon they'd be pretty close to each other.
as i said, i'm ready to be proven wrong, but this is how i understand the differences.