Alright, here is what I found when using the green spring (w/o shims). I was using my Cobb AP to monitor boost pressure during this test. Whenever the AP shows a negative PSI (I assume this represents vacuum) I can hear what sounds like air being vented through the BPV. This only occurs if I am very light on the throttle and allow the RPM's to slowly increase. As soon as the AP reports 0.00 PSI or above, I can hear what sounds like the BPV closing, followed by the turbo begin to spool. I assume this is not what I should be hearing (in terms of performance, the car didn't really feel any better or worse than it did when using the yellow spring). I think the green spring may be just a little too light for my application (switching back to the yellow eliminates this specific noise). I will say the green spring definitely seemed to eliminate the fluttering sound at partial throttle. I am going to try the green spring + 1 shim tomorrow.
EDIT: I forgot to ask, when adding the shims I believe you are supposed to place them at the bottom of the spring correct (i.e. between the spring and the piston)? A few weeks ago I could have sworn I found a thread that answered this question but I can't seem to find it.