I got matched groove tubes and I hope these are what you consider quality, they seemed costly! The ones I pulled were J/J and the sound difference is big, but the GTs I got were 'hardness 3' and the sound is still very distortion oriented I think, I can't imagine the 9 or 10 rating. So I think the J/J tubes are worthless to me as backups, I was going to see how I liked the '3' rated groove tubes and then order a full backup set.

The J/J tubes didn't appear to be biased properly either, hard to say for sure since one was damaged but it did still work just had occasional noise with vibrations that occasionally occur when playing through a Marshall :o

Anyway, i think I've successfully biased the groove tubes and will be playing cautiously for the next few weeks with the back of the amp facing me to keep an eye on them.