The NOS Mullards as you probably know are extremely expensive. I purchased a used quad of XF2's for $300. These are used tubes mind you but they test strong. The ZOTL 40 is very easy on tubes so I expect to get a pretty good life span out of these Mullards.
I think the EL34 NOS Mullards are the holy grail of tubes and yes, better than the Gold Lion KT77's. Don't get me wrong the KT77's sound great in the ZOTL40 and definitely better than the Tung Sol EL34's, so the question of is it worth the cost? It's all relative. If I didn't have that extra $300 to spend I would say no but I like to collect tubes.
I think the EL34 NOS Mullards are the holy grail of tubes and yes, better than the Gold Lion KT77's. Don't get me wrong the KT77's sound great in the ZOTL40 and definitely better than the Tung Sol EL34's, so the question of is it worth the cost? It's all relative. If I didn't have that extra $300 to spend I would say no but I like to collect tubes.