We have seen anywhere between 10-30 horsepower pending air temperatures and heat soak state. Temperature reductions can usually be seen around 50-70 degrees F. CO2 is better then water because it operates at -80 degrees and the water usually is only as cool as the engine compartment.
We just proved again that IC sprayers can be a benifit. We had a cusromers car at 400whp and 420ft lbs of torque. We hit the ic sprayer (on constant) and saw an increase to 425whp and 455ft lbs of torque. This was on a AGP large FMIC as well. So as you can see theres always room for inprovement. Yet one of the many things I keep meening to get.