Cary V-12i

There are many fine power cords among those recommended here on Audiogon. One that I have found excellent is made by the iconoclast, Pierre Spey, of Mapleshade Records fame.
I do use it for my tube amps. and it seems to increase the black background, transient speed, and overall dynamics, as if it's letting more power through. Seems to bring out a dramatic capability to complement my tube equipment's beloved natural and musical quality.
On their website, it is the top of the line model, Clearview Double Helix Mk II Power Cord Plus Version.
Even the name of the cord gets you ready to hear great things :>)
I have not heard the upgrade you ask about. But, as a start, have you called Cary to talk to their upgrade guru?
If I recall, his name is Kirk, and is easy to communicate with.

When the R version was first introduced the upgrade was $500.00. The R version is so much better it is scarry! When people found out how good the R version sounded thet would buy an I version for cheap and send it back for the R upgrade. The cost of $500.00 made the amp a steal and Cary must have thought so too. Not long after that the price of the upgrade went to $1700.00--so I have been told. I owned an I and sold it--auditioned an R version with the oil cap upgrade. In my system, and to my ears it blew away my BAT VK75SE and my Music Reference RM-200, for what thats worth. It's all system, room and ear dependent.