both! my car picks up pretty good going from stock 16* to 21-22* but gains nothing over 22*. Cylinder pressures spike past 22-23* and even with good octane/E85 and no KR it will still blow headgaskets. Pick a pulley that you can run safely then bump the timing up to fill the gap according to the fuel your using. If you make it to 22* with no KR drop another pulley and start again.