In a 2009:
8 core 2.26
8GB RAM
OCZ 250GB
1920x1080 x 2
Using AIC AND general After Effects content I have seen:
4 layers on out 1 and 4 layers on out 2 at 25FPS (8 total layers) no FX
3 layers on out 1 and 3 layers on out 2 at 30FPS (6 total layers) no FX
I have tried the same thing however, with the same size content but content that is much more vibrantly colored and complex (like HD footage of nature) that caused frame drop.
SourceChildTODD SCRUTCHFIELD
...if it ain't broke...
gimme 5 and then don't act surprised