you should contact ,JBtrio he has killer 300bs and a Pass Labs amp he just loves. he could shed some light on the subject.
300bs get expensive fast,,the SS offers reliability and the low power pass labs might be that special enough to woo most people away from tubes.
Talk to someone who actually has experience with lots of tubes and gear, not just quotes from the internet, or full of BS,, call Joe.
He tries lots of tubes, not just stuck with the same pair for years
No one here knows more about these tubes than Joe, and he had direct experience with several Pass Labs amps used in his low power high eff system.