I just put some winged C 6l6's in my Electra dyne. The amp is 4 months old, so the original power tubes should be in pretty good nick and all the preamp tubes are still original.
I really like the Mesa STR440 stock tubes, they sound really good to me. I'd be happy to continue using them, but the new Winged C tubes are at another level. Poeple talk about "harmonic content" and "smooth overdrive" and while terms like that do not really mean much it is all starting to make sense to me. My guitars sound much closer to how they sound unplugged in terms of the harmonics and pick attack. I used to ride the treble control fairly high in order to coax out the harmonics, but have actually been able reduce the treble ny a few motches. Clarity is also improved nicely across the board.
The power tube overdrive is also at a new level. The STR440 tubes had quite a pronounced overdrive tone, I could describe it as ratty, grainy or even a bit icepicky. I not saying bad as I still really like it. The winged C's seem much tighter in overdrive hang onto the guitars tone much better. The overdrive has great crunch and is very touch sensitive. It sounds much more musical to my ears.
Where I live the winged C's are cheaper than the Mesa tubes, so there is no doubt I will be sticking with the them. I think I may even buy a few spare sets.
I have Fender DRRI which until now I prefered for clean tone. The DRRI has a very sweet tone is actually very similar to the ED (ED clean is based on the Fender black face circuit). The DRRI tone was sweeter than the ED, but not anymore. I can't wait to replace the stock DRRI tubes with some good ones to see if it can claw back against the ED.