I forget who conducted a test, but i remember the results. N2O kits and CO2 kits both provide roughly the same cooling temperatures to the IC giving you some extra horsepower... but the N2O kits give you more and the CO2 kits can actully kill your power. Heres why:
It is unknown to most people just how much air is pulled into the motor at WOT and exactly where its coming from... but believe it or not it pulls air from several feet in every direction from that spiffy cone filter you run!
So what is happening is, the N20 is cooling down your IC, but naturally its displacing ambient air under the hood, and some of it is finding its way into the motor, giving you that extra bit of somehting. The C02 on the other hand, is doing the exact same thing, but when it enters your motor, it just bogs it down.
When this group of people decided to place a 15ft extension on the intake of thiere little honda civic and place the filter for it through a wall and into the next room... when both setups were used, the gains were almost identical.
So, if youre going to use N20, only use it while your running WOT, and be running on the rich side for that extra little bit thats going to make it into the motor. If youre going to run the C02, only do it at a dead stop, so that when youre ready to go full blast, your motor isnt trying to breathe it.