The two things I have learned while I am tuberolling my three amps are how little correlation there is between price/reputation/expectation and actual sonic performance, and how much sonic performance depends on the amp/tube synergy. Too many myths in the tube world, and here are several I have encountered:
1. NOS 5751 is better than 12AX7.
5751 has lower gain (70%) than 12AX7. Using 5751 softens the sound but also reduces transparency. If there is excessive brightness, then 5751 may be a band-aid, IMHO. It sounds different, but not necessarily better.
2. NOS WE 2C51 is the best 2C51 tube.
WE invented 396A tube, whose specs were adopted by later 5670/2C51 tubes. It is widely said that NOS WE396A is the best in 2C51 class. Out of four 2C51 compatible tubes I tried, WE396A is the most expensive and the worst sounding (noisier and brighter), though it has rich harmonics.
3. Chinese tubes are bad.
The Shuguang 12AX7 is actually better than other modern 12AX7's I have tried (Mullard reissue, Ei, JJ). My friend also rolled a bunch of 12AX7 on his guitar amps and liked Shuguang best. Shuguang is now producing their 9th generation 12AX7. I have not seen such an effort to optimize a single tube design anywhere else. Some other Chinese tubes I tried are kind of underwhelming.
It seems to me that predicting which tube sounds better is very difficult and I would rather buy more inexpensive tubes to try than going after one or two permium priced tubes.