I'm very happy with GE.
Sylvania is a big improvement from stock tube but GE is one step further
Bass: Sylvania has a tight, punchy bass. GE has more good balance with mid, no feeling like listen to subwoofer as Sylvania
Treble: Sylvania has crisp high but not have a good harmonic. GE's treble has softer sound but better extension in harmonic and better details. For piano, violin, percussion, etc. I can hear a lot airy, harmonics and vibe of treble.
Mid: I love mid of GE! Repeat, I love mid of GE! I can hear more details, I can feel the passion of singer. It has euphemistic and sweet sound. Less forward than Sylvania
Sound stage: GE's sound stage is better. Layer of each instrument is very goods. Very good for classical music,
According the suggestion from tubeworld, I will order Amperex Phillips. And see how it compare with GE