I'm using PS Audio's least expensive cords, the Power Punch, on my Ultras -- I got mine through AV123.
These are just really nice 12 ga cords -- and no, I really did not hear a difference.
I upgraded as part of a complete power supply renovation for my system, the main point of which was separate 12 ga (20 amp down here) circuits for my power amps, my subs, and everything else. I had enough stuff on my one original 15amp wall circuit that during loud bass passage I thought I was statring to hear a little compression -- that's gone now but I think due to the separate circuits.
I'm not going to say the whole power cord thing is a rip off; I think there is audio equipment/systems out there where you can hear the differences in power cords, Nordost Valhala cable etc. ...
but unless I win the lottery I doubt I'll ever own one
What I did was an old pro audio trick -- I paid money to take my power system out of the equation. With separate 12ga circuit paths all the way to my main panel I can mentally eliminate it as an issue.
If you really think you need a new cord for some reason, and you don't mind spending a little quality time with a wire stripper, get an IEC end and graft it onto a jobsite extension cord -- pick the gauge that makes you happy as anything over 16ga is almost surely overkill.
Now, about things you CAN hear:
Have you mapped your room at least by ear to find good sub / seating locations?
Have you made any effort to muffle bass resonances, like a pillow staple gunned in each upper corner?
Have you made some effort to notch filter out your room resonances? This one does cost money, but the folks on this site are the people to ask how to do it...