I'll play! This is how I had my settings for my JTM45 yesterday. It is an '88 reissue, and was plugged into an 8 ohm Sovtek 2x12 with Eminence speakers. Normally, I use a Marshall Silver Jubilee 4 x 12 with Celestion G12-T75 (?) speakers.
Treble Volume: 3
Normal Volume: 3
I used a jumper between the treble and normal volume to bridge the preamp circuits.
This worked fine with a loud bass player and drummer.