I agree with Stevex, I think that once there was an ionised path the voltage required to mainttain it would drop, allowing you to pass higher currents through. It is possible that the effective resistance of the air would continue to decrease the longer the ionised path was maintained for, this is certainly the case in fluorescent lamps but that is a slightly differenct case as the gas is contained within a tube. I'm not sure what would happen in a gas that was not contained in something.
The gap would be significant, the greater the gap the more voltage would be required to maintain the ionised path.
Hope this was some help, what are you trying to use it for, sounds interesting.