RCA 5670's anyone familiar?


I have a 2 tube line stage with some stock Chinese tubes.
The sound is a bit harsh and bright.
I found some RCA's at the tubestore but the guy I talked to said he didnt know their sonic qualities as he seldom sells 5670's and has no customer feedback.
These are the only NOS 5670's I have been able to find.
Anyone ever used them?
david99