I have owned both and still have the ACS limbs. The Epic was quieter to my ear or at least a better pitch but not that much not to go to the ACS that is a good bit faster and a little smoother to pull. If you are not that interested in the high dollar high performance limbs the Epic was as good a limb for the price as any I have shot. I would also have to throw in the Black Max Extreme limb that I just shot last month, very good limb for the money.
I am really liking they acs rc limbs I picked up. Better than my Uukha ux100's were, as quiet but getting better groups. Can't compare to the Epics but I can say I am very happy so far with these acs rc limbs.
I shot the epics this weekend on my titan 3 at the Colorado traditional bow society get together. The are some really nice limbs. Its almost like they have some let off at the end of the draw. 650$ for limbs is steep but these where well worth it. Dryad is a great company also. Very cool peeps.