Re: J Boats & ratings
We raced & cruised a J/130 for many years - in the right breeze on the right course it had few peers but it certainly wasn't optimised for IRC out of the factory, which could get frustrating in mixed fleet club racing.
J boats got better clued onto IRC in the last 10 years (catching up to X yachts) - especially for lighter wind conditions when asymetric kites/retractable bowsprits on cruiser-racers over 10 metres had struggled to keep ahead (on time) on the downwind legs.
Asym kites have become more common place now but many of those newer boats / one-offs are also optimised better for IRC. The other big variable with 10m+ yachts, esp on short courses is whether your crew are good enough to sail to the rating ! Sometimes difficult to assess if no others of the same design in your fleet.