Please keep in mind that some of the effects are very CPU intensive, so the more accurate you would like them to be, the slower they will run (depending on the CPU speed). You need to tweek the effect settings to try to get to the effect you want with the less CPU usage.
Also when viewing effects, make sure you don't have that effect left open in the Flash IDE, in the browser player and in the stand-alone Flash player, because that would mean that the CPU must play all the three instances of the effect.