If you are interested in the time constant settings for the Fairchild 670, as well as notes comparing the Waves Puigchild 670 to the UAD Fairchild 670 and the IK Multimedia TR5 VC-670, I have them on the UAD Fairchild 670 page.
I would really like to compare them, so if someone could be kind enough to gift me the hardware… You can find the Fairchild 670 hardware for only $50K more than the Waves Puigchild 670 plugin.