Zefal HpX's can reliably deliver 90+ psi.
CO2 cartridges work great. If someone blows it off the rim, either they've got the wrong size cartridge, or they may have pinched the tube when they put the tire back on.
A 12 gram CO2 cartridge is plenty. What I do is to use the frame pump to get things started, double-check to see that everything is seated well at about 15-20 pounds, and then finish it off with the gas. That way you let the cartridge do the hard work, and you get to be certain that everything is okay before you give it the big push.
This time of year a CO2 system can literally be ride-saving. If you have to stop toooo long for a flat change you can get awfully cold if you've been riding hard.