The clutch assist spring has nothing to do with rev-hang. Rev-hang is the result of the ECU programmed to maintain RPMs when you release the accelerator.To get rid of that rev hang isn't tune related. You need to remove the clutch assist spring, which is number one mod mentioned on page 1 of this thread.
Air conditioning. The extra load from the compressor can help RPMs drop faster, but only after the ECU stops holding the RPMs constant. So it's just a band-aid for the root problem, the ECUA/C?