Why not run both? I have 4 SED Winged C EL34s and 2 SED Winged C 6L6s in my Herbert. The growl is there, still dark and warm sounding, but it's got some great clarity too which is probably enhanced by the 6L6s. If I had to go all of one or the other, it would be EL34s though. And the SED Winged...