CCR Cave only for me... but I'm a really a CCR only diver, and it doesn't make a lot of sense for me to dive it OC.
Until about a couple of years ago, I had 12 open circuit dives, basically OW+Nitrox, and the subsequent hundreds were all rebreather dives. From my time in open water, I basically knew that was the way I was going, so there was little point to me doing full cave o/c and then trying to transition.
I've gone back since and done a bunch of monkey diving, and a couple dozen dubs dives, just to remind my back and shoulders of why I don't blow bubbles
CCR Cave covered a set of procedures and rules that both were not covered in Mod 1-3 of CCR class, nor would be covered in OC Cave, as they're not relevant to OC diving... On the other hand, in the course I took, I think there'd also be a lot of overlap - trim, navigation, drills, etc would all seem to be the same, for instance. There was a fair bit of CCR specific stuff in the overhead environment, though. I'd call it fodder for a day or two long crossover course, at least, although I didn't feel (not having O/C Cave) that it'd be like ab initio training.