As far as i'm aware there are no catalogue entries for Ibanez Roadster 6 string guitar models above the RS300, but towards the end of the Roadster era had begun to produce some other model numbers. (albeit in seemingly very limited quantities). The RS500 appears to be the new top of the range at this point. Very similar to a RS300 in many respects (brass nut, accucast bridge, super 6 tap pickups, ash bdy, maple neck) but with one or two noticeable differences. The main difference is that it's a thru-neck model (similar to the Ibanez Musician series. The headstock is streamlined/slimmed down to what would eventually be used for Raodster and Blazer guitars. The fret board is carved from the thru-neck (so the truss rod has been fitted from the back of the neck, plugged with a skunk stripe, rather than going in under the fret board as on the RS300) and there are unusual double dot fret markers (3 dots at the 12th fret). The wood seems to be of a particularly high quality and is nicely figured. The curves are just a little bit curvier than the RS300. Subtlely so, but different. It's only a slight difference in feel between the RS300 and RS500 and both are stunners in my opinion!