I have a Cat SL1 mkIII and did a little bit of NOS (telefunkens) rolling and would agree with Ken. I had much more noticeable results tube rolling on my power amp input (and to a slightly lesser degree, power) tubes.
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I guess on different days, Ken has different opinions.
He has told me that Telefunken smooth plates are the best he has heard in his preamps. I think he hasn't done much experimenting. There are lots of tubes that will vastly outperform Telefunkens in my CAT Sig MK2. I am currently using Amperex 6922 pinched waist and Sylvania 5751 blackplate 3 mica square getter tubes in the pre. This combination is the best I have found (lots of rolling) and very expensive. Almost anyhting will outperform the Sovtek 6922 that is the stock tube in the pre. There are lots of tubes that will outperform the EI 12AX7's. If you try the inexpensive American tube types you will find better tubes than the stock tubes.
I have a SL-1 Ultimate Mark II but have previously owned a Reference Mark II and a Signature Mark III. And tube rolling definitely makes a difference. I have spoken to Ken in the past and his response was that the stock tubes made the preamp sound the most "neutral", but that the sound can be tailored by using NOS tubes. I also think Ken is insuring that the current production tubes will always be available, whereas NOS tubes will not be. I found the best tubes, to my ears at least, to be Siemens CCa's for the 6922 positions and Raytheon D-getter 7729's (just try to find these!)for the 12AX7's. I tried some 5751's and didn't like the lower gain and reduced dynamics. Ken doesn't recommend these and I can see why. Others seem to like these but I don't know why.