Hi Don,
To my ear, the difference regarding cryoed "military" SV83's makes it well worth the effort. In fact, the driver tubes and even rectifiers seem to benefit.
The 6n15n-ev's are far more open sounding across the board to my ear, when cryoed. Every now an then I regress and try an uncryoed pair, but my impression stays the same.
Yes, agreed; the "CCE mod" has taken the SE84xx amps a gigantic step up, far more so than any other tweak. The benefit is huge. I feel sorry for any one using a similar type amplifier that is restricted to EL84's only (where the suppressor is internally connected and the mod is useless).
I've now incorporated the same mod into an old ST70 using EL34's, with similarly stunning results. I can hardly believe what I'm hearing.
In fact, now I wonder if some version of this same mod might be beneficial to EF86's in lower level driver circuits

Yes, the cryoing of the output tubes is really worth it, but get this CCE mod done at your earliest possible convenience.
Karl