Welcome aboard Rob !!!
Those 6SN7's that make the top 5 lists are indeed expensive. But there are still some very good sounding tubes that can be had for very good prices with some searching and patience. For example, Sylvania 6SN7 GTA and GTB can be found for pretty cheap and I dont find them having to apologize all that much to the Sylvania VT-231's which are on most of those top 6SN7 lists and are usually far more expensive. I've also found a few relabeled Sylvania VT-231's for cheap. Of course all this is ear and gear related so YMMV. But you sound like you are in good shape with your stash. Just pointing out that, depending on which tubes you fancy, there may still be some bargains out there.
BTW, I was running a 6SN7 in Crack with an adapter. It was my preferred tube when Crack was a stand alone. I built Foreplay III for 6SN7's and running in front of Crack, went back to 12AU7 or 12BH7 in Crack (currently 12BH7) with the 5998 output tube. Good advice offered about initially building Crack stock with the 9 pin socket. You can use a 12AU7 to 6SN7 adapter to roll your 6SN7's and compare with 12AU7 and compatible drop-ins. You never know what you may end up doing in the future. I also considered replacing the 9 pin with an octal socket in Crack. Im glad I didnt because, as mentioned, a I expanded the headphone system I found that I preferred the 9 pin driver tubes in Crack when I built FPIII for 6SN7's. You can always enlarge the hole later but it is a bit tight as is already, as Paul B. mentions.
