here's a little more info for you,
http://www.powertank.com/charts.specs
I built my own C02 system for about $120. I am know running a 20lb tank and it fills my tire(1) in about 30 seconds. I normally air down to about 12-15psi. I run 285/75/16s at about 35psi on the road. According to the powertank chart I can fill 40 tires of that size! I didn't see the air tool chart, but if I recall a 15lb tank could run a impact for about 8 mins(continously) or remove something like 100 lugnuts. The refills cost about $15 and can be done at any fire extinguisher supply store and many paintball and 4WD supply stores as well. It is also portable so if your buddies rig breaks in the middle of the trail, you can just carry it up and have him up and running in no time. It will also allow to reseat a broken bead, which is well beyond the capabilities of most compressors. The liquid state of the Co2 allows for much more volume than a comparable size air tank and is much safer than you think. The tank is only under about 300psi of pressure, which is just over twice what a air compressor will put out, NOTHING like a SCUBA type tank which can be 3000-5000 psi (steel DIN tanks). A Co2 tank will not shoot through the side of your rig even under the worst case of you whacking the valve clean off. Besides the fact that you can easily protect the valve from damage with a guard.
Oh well there's my $.02 and then some.
I do check my tank by weight before any trip. (the tank gauge is useless on a Co2 tank BTW it measures pressure which is constant! NOT liquid volume.).
But if I do happen to run out you know I love you guys with the bling onboard air compressor/tank set ups right?
Cheers
Vince