Honestly I would try out the Sylvanias you already bought, they might give you what you're looking for. You can get them cheaper than the price you paid but they are still good tubes. Sometimes the price is determined by rarity, not necessarily by how good it is. Some of the tubes that go for high prices I think are pretty mediocre. There's nothing wrong with the Sylvanias you bought so give them a spin before spending more.
I got both today and I am trying the Sylvania tubes right now. Immediately I think they lend an improvement to soundstage. Instruments are much more left/right forward/back as they are supposed to be, it's marked over the RCAs I had in there before. The RCA lent a bit of warmness, these still are a tad warm but not as much. I like warmness to a degree, and the RCAs were IMO good, these are better though. The warmth is somehow more tasteful? restrained? I don't know how to express it, but it's warm when it needs to be? As far as SQ, they have shown taut bass & airy highs without any glassy bits. Digging them so far, I guess I am obligated to since I overpaid !
I still like the RCAs, however they will be demoted to backup after today. I have yet to try the GE tubes, maybe they will be OK too, but I'm in no hurry.
Edit: By request, here are some pictures of the Sylvania GTBs
Edited by toschek - 4/11/13 at 2:03am