$50 for a more or less gaurunteed tube of that age and scarcity is a very reasonable price. In that application, I really don't think you need to spend the extra money for the quieter tubes. Obviously YMMV etc. try the standard grade and see for yourself.
FWIW The RCA triple mica blackplate is indeed a very good 5751 but not particularily warm.
FWIW The RCA triple mica blackplate is indeed a very good 5751 but not particularily warm.