I think the stock power cords are pretty damn good. Better than most stock power cords. IMHO, power cords make less of a difference on the amps than on preamps and front end components. I've used Shunyata King Cobra V2's, Elrod EPS-3Signature's and currently Cardas Golden Reference on my M100's. I kept'downgrading' money-wise to put the money elsewhere in my system. When switching back to the stock cords I was always surprised by just how good they sounded. I only went with the Cardas GR p/c's because I have my M100's plugged into a Running Springs Audio Duke power conditioner, which uses a modified 20A Cardas Golden Reference power cord and has Cardas internal wiring as well. Sort of a synergestic thing.
I would say there are better ways to spend you money than upgrading the M100's p/c's. Spend it on front end or preamp p/c's or interconnects, or just music.
Regards,
John