I owned a pair of Cary 805C. The NOS tubes for those are hard to find and too much money to buy. I had all kind of tubes to listen to. The 211 RCA tube could bring the best sound. But you have to call Kirt from CARY to ask for the diagram to mod. the wire under your 845's tube socket. Otherwise, if you could find a Chinese name "Golden Rragon". The 300B Tube, with Cary Amp the NOS was not really upgrade the sound much. The Chinesse 300B give u more Dynamic sound and more detail. The Western Elc. give u bigger soundstage and brighter high frequency. The 6SL7 is only tubes u need to upgade with NOS for sure. Kenrad or RCA red base are the best. The tube set I used right now were the Golden Rragon 845 and Golden Dragon gold pin 300B and NOS RCA 6SL7 red base, the price for this set is about US$400x2(2 set for single ended Amp). My best sound was those 805c here, even i owned all the Amp over $20K tube Amp still couldn't compare with, and any kind of CD or CLP you insert to your system could make you crazy about its sound. Think about NOS 211 and 300B, you have to pay 5 times more and the sound just sweetter on vocal, but less Dynamic.
My system had a Audio Research CD player, Rega CLP, Cary tube pre-amp, Cary 805c, and ProAct 3.8 speaker. My listen room size was 18'x25' .