Originally Posted by WhyFi

There's probably less differentiation than they'd like at this point, the Caledonia 5 was developed at a time when the R3 and R5 officially maxed out at 28mm tires, but there's probably still some comfort/compliance differences and some small stability/agility handling differences. The R5 is their all-out classic race machine - I know that their pro riders were complaining that it was too stiff, particularly the front end, so they made the new R5 a smidge more forgiving. That said, it's probably still stiffer than the Cal 5, which has sections of lower mod cf, iirc, and the dropped stays, both for compliance (and maybe a little aero on the stays). They made a point of mentioning fenders for the Cal 5, too - not sure if they have mounts for them or not...

The regular Caledonia probably makes the most sense for most people. The Cal 5 is there for the up-sale. The R5 appeals chiefly to the racer-boys.