anytime you can run a guitar amp with little or no negative
feedback, it means you've learned how to build a killer preamp and
are mastering the blend of preamp/power amp distortion!
Go for as little NFB as you can for the richest musically harmonic
power tone.
Use the NFB as a tool for tweaking the thing and eventually you'll
find the right amount of NFB that suits your playing and you ears.

6K is a very good compromise for EL84s or 6V6GTs.
I've had really good luck slapping in a generic TMI or Thordarson
reissue Deluxe Reverb OT, (abt6Kohms/8ohms), into a number of
EL84/6V6GT amps.
I think they work slightly better with fixed bias and with cathode
bias I seem to favor a little higher OT primary zed.

Bruce