for what it is worth I did a a few observations in rgrds to different tubes in my Blue Hawaii before I change the CSS in the output for a T2 style CSS..
I have three sets of matched quads EL34's: 1 new set of Harmonix's and two NOS Mullard xf2 db getter brown base
There are quite a substantial difference between the Harmonix and Mullards to my ears, whereas I definetely prefere the latter.
As I recall the amp behaved very differently looking at the scope. At 1 and 5kHz squarewaves at various levels, the Harmonix seemed to behave less optimal and seemed to introduce more phase shift in comparison to the Mullards. Especially at high volume levels the Harmonix seems to loose their breath quite quickly.
As mentioned these are only brief observations but seems to support the observations from a lot of other people, @mulveling, @arnaud, @purk among others.