I've used both the RMR and 507K and have a preference for the 507 due to seeing more of a crisp dot with my astigmatism. The side loading battery and slimness of the optic is awesome too.
As for the RMR, I can still use the dot reasonably well, I just have to turn the brightness down for shots at 25 yards.
As it stands right now, I'd choose the 507K over the RMR. Is there another factor that might warrant sticking with Trijicon rather than Holosun?