Paul,
Right now I'm trying out some EI Yugoslavian tubes from the 60s or 70s that a friend gave me. Early impression is not a profound improvement over the stock JJs. No cash for fancy-priced Amperex right now.
In my CAT pre, (years ago) I favored the Amperex Bugle Boys over pricier Teles & Mullards. The best performance/price ratio went to the Tungsrams.