I'm also very interested hearing this! Stock Mesa 6L6 vs. SED 6L6??
A Finnish internet tube seller (www.uraltone.com) suggested me SED 6L6 tubes for Mesa. They said that SED are the best tube manufactured today. And that New Sensor is now manufacturing tubes with name (Svetlana, EH, Sovtek, Tung-sol) and their quality and sound is worse. Since Mesa is only interested in how long tubes last, I'm looking for best possible sound. SED is closest thing to NOS and best part is that this store measures tubes, so I can put them straight to my Mesa Stereo 2:Fifty without changing bias. I probably have to try EL34 also in my power amp to see if sound gets even better on overdrive channel..