I have / have had several Mullards and they may sound different as it often happens with NOS / vintage tubes. My gold standard is a pair of (apparently) genuine NOS CV 491 from 1957, Blackburn factory, which have that trademark Mullard sweetness in spades while retaining more than decent technicalities.
G73-R is a
special series of ECC 802S from Telefunken, which was made in the '60s specifically for Agilent and HP, both military and medical applications, targeted to very strict electrical tolerances, thermal stability and enhanced mechanical robustness.
There are variants of this tube, with red and with black print labels. I have one sample of each, and, yes, they sound
different.
Compared to Mullard, the G73-R(s) are indeed faster, more dynamic and transparent, while not being harsh, dry or bright. Mullard has more bloom and euphoric midrange richness, while G73-R delivers a big, holographic 3D picture and a tighter bass. Top end extension and liquidity is also excellent on the Telefunken.
For my personal tastes and for the music I listen the most (classical, unamplified acoustic jazz and vocals) I find the Mullard more pleasing with the AB-1266 TC and the G73-R more with the Valkyria. Actually, the "red print" G73-R / Valkyria combo is my overall preferred setup.