I would love to have a dry suit, but dropping a grand on the suit and then adding undies, etc. is out of the price range right now. I have found that the John/Jacket seems to be the better price performer, even if less comfortable. I like the idea that a j&j can be separated if needed in the summer. The quarries are pretty cool year round and I'd love to spend some time in the springs around Ponce De Leon, FL but if it gets too warm I could pull the jacket or vice versa. If you're using a standard BC, mine was 5# positive. The SS BP is 5# negative, that's a swing of 10# so I shouldn't have to wear much extra weight.
Drysuits are expensive. I am actually taking the class to be able to try a few different drysuits on first and hoping my wife will release the funds to purchase one sooner or later.
I actually like my farmer John suit better than my one piece 7 mil. The overalls and jacket actually fit snug against my body and I get less water movement. That seems to help keep me warmer longer too. I agree that the two piece is more versatile and you can easily adapt it to diving conditions.(yes, quarries are cold. I took my farmer John down to 45o in one here in GA! Forgot about that dive.)
My next upgrade after my drysuit will probably be SS B/P and wing! That would put me near weightless in my normal 3 mil wetsuit and cut more off weight off the other suits I dive.