There are regular Sovtek 6922's and there are the flat gray plate Sovtek 6922's, which are very much better, but certainly not the best, IMHO.
I would search around for some folks who have your particular preamp and, if you're lucky, at least close to your other components. Even they will only be able to give you general guidelines as the 6dj8, 6922, 7308 tubes are very system and component dependent. Also, the 6n1p is a cheaper option which some have found superior to many of these other tubes in some applications like preamps (check with the mfg., though, because 6n1p's are not necessarily interchangeable in all cases).
Sure, the Siemens and Teles mentioned will be sweet sounding - IF they are the real thing, IF they are the proper vintage, IF they are closely matched, and IF they have been tested closely with respect to microphonics. Dealing with a reputable and honest tube dealer will eliminate some of this anxiety. Might be more costly, but worth it in the long run.
Many other manufacturers have made great tubes in this family - Mullard being but one other not mentioned. The US-made White Label Amperex PQ's can be very good.
All of this said, even the best of the best of the Teles, who some will say are the best for everything, may not be the best in YOUR application. I have had more than a few components based on this tube family and was sometimes surprised at what sounded best. For instance, I had a Kora Eclipse preamp and I tried about a dozen different tubes in it, some being the very expensive varieties of brands listed here. In the end I found that the best for that component, in my system, and to my ear was a trio of La Radio Technique 7308's. Go figure.