I have a pile of antique 6SN7s (name the American, European or Russian brand, I've probably got a pair). At least in the octal iterations of the SP-14 and M-125 drivers, the Chinese PSVanes and Shu Guang Black Treasures will blow the doors off anything in the inventory. They take several dozens (some say hundreds) of hours to fully develop, but even out of the box they are amazing. Muddy at the top for the first few hours, but at start-up produce a nuanced, detailed bass that doesn't go away as the mid and treble ranges develop. A caution: the PSVanes, at least in the octal driver slots of the M-125s, do generate a hum when new. This may go away as I burn them in in the SP-14. They are dead silent in the SP-14. The Black Treasures have no issues in the M-125 driver slots and are great in the SP-14, but damn near twice the money as the PS Vanes.
Either tube is a fraction of the price of a rare U.S. 6SN7, and worthy of consideration. Prices are climbing daily.
One danger, Will Robinson, Beware: these are huge tubes. They may not fit into your enclosed preamp cabinet and are virtually touching each other on the sides -- the latter is no problem but you may need to take the lid off the SP-14 to accommodate their height.
Unless I see one or more fail at the 500-hour point, these are going to be my go-to preamp and driver tubes.