I instantly liked the sound of the tubes and preferred them over the EL-34's I have used in the past. Even before breaking in, I noticed a much improved sound from my ST-70. Stock board running 7199's by the way, so no way to compare them as far as using a VTA board. I biased at 75ma per side. I read that I could bias them even higher but I just think they sound excellent where they are. The Gold Lions hold the bias rock steady in my amp.
Now after all this time, and the tubes are WELL burned in, I decided to do some tube rolling in the amp they were in to see if I was liking the sound because of the money I spent, or if they really do still sound better to me then the EL-34's. Hands down, without any reservations, the Gold Lion KT-66's sound "better". I compared them to my burned in Svetlana's and my Winged C's. They are absolutely a better sounding tube in my amp and to my listening ears (which are old and wore out by the way LOL).
I am pushing a couple of KG-4's (4ohm) and also hooked up my Heresey's (8 ohm)to test with. I love my Klipsh speakers, and I don't have any extremely high priced speakers to test with. I don't have a clue how these would perform with Maggie's or other types of speakers, but in my system they are the best tubes I have heard to date.
Just thought I would give an update on how I like the tubes after all this time, and how they are comparing to my EL-34's after being burned in. I still have to give a complete thumbs up to the Gold Lions. Especially in the high end, they sound crisper, cleaner, with more openness in the stage.