Greyhound was nice enough to send me a few sets of 6CG7 tubes to try and I thought I'd share some results. I rolled tubes in the preamp.
I have AVA FET preamp & 400R driving Revel F52's and a T+A CD Player.
Tung Sols; I did not like them, overly warm, very rolled off with soft bass response.
Mazda; were pretty good, excelled in high frequencies that I thought tonally accurate, grain free and easy to listen to while being extended. This tube gave me the impression of being very fast, meaning you could hear between strikes of fast drums and between notes of guitars very well. Seemed to me although not lacking in bass the bass line was sometimes buried.
RCA Black Plates; These were very nice, extended highs, full bass that remained defined a natural warm midrange with good presence.
Sylvania Gray Plates; A hard choice of favorite between these and the RCA-BP but in the end I preferred the Sylvania. The Sylvania is a very dynamic sounding tube, good presence in the midrange, the bass hits good yet very controlled. The high end is decent but not as foward as the RCA.