well a RG1527 is not a J-Custom. J-Customs that i've seen are a bit nicer than the RG1527. dont get me wrong my favorite player used a 1527 every time i saw him play, but its definately not a top of the line 7string. i havent had a chance to play one, but i've looked into it extensively.
i owned a RG7420(korean) for about 4 years and loved it, i currently own a RG7620(japanese) and love it even more. the RG1527(japanese) has had many reports of paint chipping off easily, which i had the same problem with the 7420. the 1527 i dont think has gotoh tuners like the 7620 has, i think theyre just standard no name tuners. and the 1527 just has the standard V7 and V8 ibanez pickups, where as the 7620 had dimarzio pickups that were clamed to be Blazes at first but later found to be some designed by dimarzio thing. both have the wizard prestige 7 neck, but the 7620 is a one piece and the 1527 is a five piece.
either way, i love ibanez 7strings, but i bought my slightly beat up 7620 for almost half of the cost of a 1527, and it plays and sounds just as good if not better than what i'd expect from a 1527. i'd vote for buying a used rg7620 and use the extra money for straplocks and pickups.
or just buy a caparison, theyre the only company who's 7string i think i'd want more than an ibanez.
