littletoe is right that is the correct air calculation when 1/3rd of your air is up back you go NO EXCEPTIONS EVER EVER EVER!
as to buddy breathing diving with a buddy in a cave simply increases the danger in my opinion VERY rarely do buddies manage to help someone out yet in almost every single cave diving fatality (at least in florida) the problem stemed from a buddy type problem trying to air share or some other thing I NEVER dive with a buddy ever even openwater. Now don't get me wrong this is a controversy (not as big as bush vs kerry but hey that one will be over in a few days) some people swear by buddys others such as me say take care of your own booties then let others take care of themselves...
As to carrying a spare air or pony bottle most of those are good for "free ascent" or "open ascent" from 100 ft or less, in fact many even have that on the lable. Trying to swim horizontally for 200 ft then verticaly for 30 ft on a spare air that has anywhere from 10-20 breaths on it at 33'...? Not me, thats pretty scary stuff. Also I know these aren't your pics but the pics show people swiming through restrictions how are you going to buddy breath through those on a three foot octo hose?
Lights too never ever go into a cave with only one light even a dual bulb lantern what if an "o" ring fails and the battery compartment floods and shorts... night time... I wouldn't go into a cave with less than 3 lights and usually a chemical light stick or two in the old dry suit pocket... I've talked to some of the old cave divers here in florida about the old days when they would wrap a regular flashlight in electric tape or put in in a canning jar to keep it dry in a cave... I've actually had nightmares after talking to some of these crazy people!
Insofar as saying cave diving is "insanely dangerous" if you take recreational equipment which is extremly prone to free flow, and breakdown into a cave you are INSANE if there is someone two feet from you who is completly outfitted for overhead and your wearing a jacket style BC with a dive rite reg and some mares fins and mask complete with snorkle (I wondered what they were doing with snorkles in a cave... I guess the holes between caves were snorkleable... is that a word?) anyway if you go into a cave like that you are doing something crazy! Thats like skydiving with no reserve and trying to shoot skeet though your main parachute on the way down... yup you might make it, or you might just die!
I dont' mean to sound like a jackass no it all but so many springs have been closed to cave and cavern divers because recreational divers get into them and get killed. I would hate to see anyone get hurt so the pics were great but please do be careful!
As to the springs I live about an hour and a half from ginnie but I'm currently not diving as I am so broke i squeek when I walk! maybe by next winter I'll be back in the water! cross all my fingers and toes!!!