I think they are only limited by the rest of the system. amps probably aren't the limiting factor. I'd think speakers would be. I have a pair of $3000-3200 ASL monoblocks (1006-845) with probably $1600 worth of NOS tubes in there...yes, significant differences to be heard. I don't think you could have overkill, really. I have a pair of EL34 Mullard XF2, and also a pair of early el34 Teles. I've thought of buying a pair of ASL single ended EL34 amps just so I can hear these tubes in their glory. (or maybe build something). the CJ Pr. 5s take 8 EL34s per side, so either I need different amps, or a hell of a lot more vintage el34s (not going to happen), or I just sit on them for now...
Personally I think there is more difference between various tubes than there is between various amps (to a certain degree.). for example, a $3000 pair of ASL monos with NOS tubes is a lot better value than a pair of $25,000 Viva Aurora or Cadence 845 amps, no matter what tubes are in them. IMHO.
BTW all the Jadis I have seen has just been sidelined gathering dust in the repair shop, waiting for parts and info.
_Ed