Hi Sean,
I've done Gages, McFails, Onesquethaw, and a few others around that area - all with a 3mm one-piece full-length suit worn under my nylon coveralls. Of course with those caves you're in and out of water, and not doing anything silly like cave diving.
I owned a 7mm jacket and pants years ago, but I found it too cumbersome for this type of caving. Even the 3mm is a bit of a pain when ascending up the waterfall in Halls Hole. It gives the muscles a good work out, though!
One time on a slower trip, I experimented by wearing my thin polypropylene long johns and top underneath my wetsuit. That seemed to help a little with the warmth. (I deliberately bought my wetsuit one size too big, to allow for caving activities.) I use neoprene and rubber "Muck Boots" in wet caves, along with neoprene socks or thick synthetic ones. They work great. I also have neoprene gloves that I got on sale from Wal-Mart. I chopped the thumb and forefinger tips off so I can operate my camera and surveying instruments with my gloves on. For extra warmth, wearing a balaclava under your helmet is a good idea too. 8)
I can't recall the water temperature in Scott Hollow, but I don't think it was all that cold. I was in there a couple of years ago. It wasn't a wetsuit trip, but we were in the water for a while and I can't remember being cold.
Have fun...