Using effects and a crossfade together can make it nessecary (hmmm, I always forget how to write this word...) to render everytime you move the clip, because the crossfade parts needs to be recalculated.
But in this case it sounds like the effects can't be done in realtime: they need to be rendered.
And because you are stacking 2 clips with effects: the preview needs to be rendered everytime you move it around.
(The previewfiles are clips, not seperated frames. So the whole clip refers to a certain selection with certain properties. When you move a clip back to a previous situation, it should turn green, because it remembers there is a previewfile for that.)
You can try what happens when you disable one or more effects.
This is exactly why colorcorrection and grading are in the end of postproduction: too much render time when you keep changing things.
@Sweetie:
keeping up is important indeed, but for what H44 is working with CS5 should still be sufficient.
Under 2 conditions:
1) the hardware isn't a bottleneck
2) the user should have a clue of what (s)he is doing.
If the latter is false: the newest version won't help.
(And if the first is false, the newest version won't work

)