Lamm ML2.1 Tubes

Hello, I run the ML2.1 with the tubes from factory and I am interested in opinions about using it with NOS Tubes.
Compared to the stock 12AX7 I tried NOS Telefunken 12AX7 and Mullard CV4004. There are differences, but nothing dramatic (in my opinion).
Are NOS really worth it (in general) or did someone find the match to go?
Thomas the new reissues New Sensor - Mullard ECC83/12AX7 and CV4024/12AT7 tubes in my MC275 amp provided another layer of details. However, my Black Sable - Mullards ECC83/12AX7 in my C500T preamp made the most sonic improvement...and they were the most expensive!

Later this year I will revisit NOS 12AX7 types that improves midrange and bass.

On a different subject, changing the fuses in the MC275 also improved the sonics.
So far, the Tele 12AX7 ribbed plate is best in my ML2; many others prefer the smooth plate Tele, but I've not tried that yet. I like the Mullard CV4004 in my phono stage, but did not think to try it in the Lamms...hmmm.
I have preferred my Telefunken ECC803 tubes in my ML1.1s, but I think one of their main advantages is their longevity, the sonic difference being noticeable but not a huge improvement over the already good sounding tubes I had in there. I remember asking this question in the past and the question asked back at me was what is that you want to change...I think that's something you really have to ask yourself. If you like the sound of the stock unit, I guess you should think twice before shelling out the big bucks for NOS tubes. On the other hand, if you have some spare NOS tubes sitting around (having just sold a 12AX7 based preamp and amps I had a load of leftover and new spare Teles), tube rolling for the Lamms is a simple exercise.
Thank you Pierre for the New Sensor - Mullard ECC83/12AX7, didn't know that.
Thank you Triode, I will try to get some info about the difference between ribbed/smooth plate.
Thanks Rcprince, too. Well, honestly I don't want to change something, probably a bit more of everything. I have some Tele 12AX7 from my former Aesthetix Callisto, they've been really expensive. I listened to them now for 2h and yes, they are different to stock, but the price is 10x+ ....
I have the same opinion as you. After trying NOS Tele's and NOS GE's, I've decided the stock tubes sounded more like I wanted to hear. I must not have those golden ears or in the Lamm ML2.1 circuit design there's no improvement to be gained. I'm not selling those Tele's and GE's just in case.
I prefer the Amperex 12AX7 long plate D getters in my ML2's. These seem to have the best combination of clarity and bass. I liked the midrange of the Telefunken smooth plates but theywere too light in the bass in my system. Unfortunately the Amperex will set you back a few hundred dollars.
Dear Gerry, yes, the "Upgraditis" is like a wave, up and down, thank you Dmailer for your experience, Amperex is an interesting choice.