Make sure you separate, in your thinking, the concept of the a/c feeding cold air directly into the intake, versus the a/c cooling the intake plenum, or cooling an air to air heat exchanger, like an intercooler. The trade off of the energy used to the energy gained is different for each method. As describer above, the a/c cannot supply enough CFM and pressure, so that's out. What it can do, is cool the intake air by some form of heat exchanger. Some cars have the coolant routed around the thottle body, to reduce intake temps. If that's viable, then cooling the intake with a/c air, (or even the R14 in a liquid to air heat exchanger), would be even better. Sure, it takes power to run the a/c, so you might write it off as a zero sum game, but remember that concept doesn't apply universally. A roots supercharger can take 100hp to run at redline, (case of the Ford GT), but the power added gains exceed the power drained. That's not a zero sum game. What you would have to study is the limits of sustainable gains in varying designs or liquid-to-air or ait-to-air heat exchangers, the heat soakability of the a/c system. Of course its going to get loaded down beyond its design parameters, but what gains can be had, and for how long? Those questions need to be answered before the idea is written off. Or you could do like some drag racers do, and load a block of dry ice onto your intake manifold just before a run. (Not the same thing, I know, I know)