yes red base and some VT-231 are the ones I like to compare with the CV181.
I was very lucky this Mullard becuase my NOS tube dealer offer me as a "bocatto di cardenale" but I really don't knew it,so I have delay my dicision for a week, meanwhile I have asked on the forums. Then PQ answer me and I have get one of the 5 he have. Then I have think in get a second, but unfortunnely, he sold all on that week. The best part was he sold me the tube in a ridiculous price, compared with the cost on tube depot or ebay. The bad part, since then, he never had again another bunch. This tubes are absolutelly rugged and sound really great. Of course, I don't know if all production years are the same in quality, but mine are stunning.
Since your post, I have change for a while with my Brimar CV1988 to compare, and sound great also, but I prefer the CV181 absolutelly.
Hope I can get soon some red base to compare.
Best for you,
Beto
P.S. Now I'm enjoying a pair of BRimar CV4004 on my phono stage and sounds great (well, compared with the original Ei) I will get also a pair of Mullard and Telefunken soon