07-13-14: Ivan_nosniborJohn ("Ivan"), and I say this with respect (given the many knowledgeable and helpful posts you've made in the past), none of this is true. Degradation in performance that may occur as a result of AC voltage that is too high or too low does not occur because "more noise slips past the cancellation circuits." It occurs mainly as a consequence of the voltage change itself. And regenerators certainly do dramatically reduce noise (and distortion as well) on the incoming AC, although of course not to an infinite degree.
... the closer you get to the edge of that 5% window (and beyond), the more noise will slip past the cancellation circuits and affect the sound...that general malaise that tells you it's feeling kinda sick (and not in a good way). This is why people feel like regenerators reduce noise, they don't per se....
As far as the OP's question is concerned, you've received several good comments but I'll particularly second the one by ZD. There are way too many variables and unknowns, involving the designs of the specific components in the system; the voltage, noise, and distortion characteristics of the incoming AC; and the designs of whatever power treatment candidates you may consider, for anyone to be able to predict what choice would perform best for you. Not to mention what choice would provide the best tradeoff between performance and price.
Regards,
-- Al