Tenor 300HP / 150HP Tube Rolling

Anybody try swapping out the stock ECC83s with NOS Telefunken, Mullard, etc.??
My understanding and expectation is that the $9 JJ Teslas can be bettered by several of the legendary NOS names like Telefunken and Mullard. People usually won't replace perfectly good stock tubes with "Old Ones" that cost 10X times the price withuout gaining a significant improvement. This practice is regualarly done on tubed pre-amps and phono stages.