I tried the EI NOS tubes. The clean ch sounds much better with Ei tubes but I like the OD ch more with Tung-Sol tubes. Ei tubes are much clearer (more hi end and better bass definition), I could say more HiFi sounding but you lose that smoth tone which you get with Tung-Sol tubes.
I also tried Ei in V1 and Tung-Sol in V2 and I still prefer OD tone with Tung-Sol in both positions.

 

Fortunately I have a very large supply of NOS and ANOS tubes, so I did not order my amp with tubes. Proper tube selection can make a big difference in the tone and response of most amps. V1 is going to be the most important in the Overtone as it affects both clean and OD tones. Spend time going through various tubes, checking for tone and microphonics. It's probably the most important tube in the amp. Bugle Boys, RCA's, Mullard, and Telefunkens work well here, but long plates may be somewhat microphonic unless you sort them. I've found EI's to sound a bit jangly, and like them better in AC30's than D-type amps.

V2 will be your OD tube, so also go through the same process there, focusing on the range of OD drive and microphonics at volume. Make sure you have your trimmer set properly as that makes a huge difference in the character of the OD. Too high will be harsh. You may want to re-select tubes here if you make a big change in the trimmer.

After that, I often will like a GE 5751 for the phase inverter, but try different tubes because in that position relative balance between halves can make a difference. They don't have to be matched, but they will sound different if they are mismatched from one side to the other.

For the power tubes, RCA 6L6's sound really good in the Overtone, but may not be worth it if you only play lower volume. I've had good results with Tungsol 5881's also. Good NOS tubes will generally sound better and last much longer than new production tubes.

What about different power tubes? I heard somewhere Carlton uses Sovtek 5881 tubes in his Dumbles for more dirt and crunch?