My experience with ACES IV:
2 fill up on the SHO, not much to report, I probably have to reset the computer or re-tune to benefit.
3 fill up on the WRX and WOW! It's a 2L engine with a 20G turbo so low RPM was pretty dead on torque but since running ACES IV, the part throotle low RPM "get up and go" is much MUCH improve. Turbo is faster to respond and the tail pipe seems to be cleaning itself. This is all happening in the "close loop" part of the tune, where variable valves timing is in use. When going WOT or higher boost "open loop" tune, not much has changed. So a dyno re-tune for the open-loop should help benefits from the ACES IV, I guess. But at a 10.8 AFR, the tune is too rich anyway.
Running Petro-Canada 94 octane in both cars.
EDIT: forgot to say, the WRX engine is running smoother too. It was already a happy reving well balanced motor (EJ207) so I am impressed!