No tube is worth 4k i would not buy anything on ebay as its pure crap.
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"I like the 6F8G's which require an adapter much better then the 6SN7's but better still are the Marconi BL63's which also require an adapter. Before using the latter, you need to make sure your gear is up to the current demands of this wonderful tube."
Just to to point out the OP was which is the best 6SN7. Hel-loo!
To future readers - WS_Trader present the facts not opinion
When making these statements it would be helpful to include a data sheet showing where they are the same. Here are a few key difference.
Output capacitance on the 6J5 is 3.6pf versus .7pf for the 6sn7. Lower is better
Power handling for the 6j5 is 2.5 watts versus 3.75 watts per side 6sn7
The 6sn7 tube can handle 4.9vrms input versus 3.2 vrms for the 6j5.
Not the same tube