CAT Ultimate/Tube rolling

Anyone had good luck switching tubes in the CAT and found the "ultimate" combination? Telefunken? Mullard?
To all,

In your experience, is the CAT pre rough on tubes. One of the apparent virtues of the Sovtek is that it is a long-lasting, reliable tube.

How do NOS tubes do with this preamp in terms of longevity?
the CAT Sig Mk1 USED to be hard on tubes. Back then Ken Stevens used 12AU7 instead of the 6922.
Then came along the Sig Mk2 wherein the internal cktry was changed & the 12AU7 was thrown out & replaced with a 6922. Ever since that rev, the CAT uses 6922 tubes.
It NO LONGER is hard on tubes any more than any other tube pre out there.
For example, I've been using the 6922 & 12AX7EH tubes since Nov 2001! These were used tubes. Now I need to send the unit back to CAT for re-tubing.
I have no info on how long NOS tubes will last. However, I suspect that one will be able to get approx 2000 hrs from them IFFFFF the NOS tubes are bought from a reliable source that can guarantee them to some degree.
I think Vintage Tube Services' website says it very well "85%-95% of Life, 100% of performance....". Usually with NOS tubes one is never going to get 100% life (you could but you'd pay thru your nose for NIB NOS tubes!). So expect the number of hrs of usuage to be accordingly less.
NOS means NEW old stock; ie, NOT used...if they are used then they are not NOS.they are simply used

true, C123666. however, even w/ NOS the skeptic in me does not expect 100% life owing to the fact that these tubes are 30-40 yrs old & the vacuum is probably compromised some. If i get full life from them, i'm very happy & it's like icing on the cake but I go in w/ the mind-set that i'm going to get less life from them.
Anyway, that's what I meant to indicate in my prev post.
I guess we need a new term UOS for used old stock!

Hey Bombay - any news on the Mullard 12ax7?