Tim Williams wrote:

Matching bias current for an equal grid, plate and screen voltage for a
self-biased class A amp, or matching Gm at equal bias current and Vp, Vs
conditions, for a fixed-bias amp. Maybe both.
Point being, Gm differences have little effect in class A amps, whereas Gm
is best matched in a class AB amp, where equal voltage swings are more
important.

Not in a guitar amp. Try it and see.

Most are fixed biased anyway (since auto bias is impossible
without compression effects),

Mmmmmm! Compression! Sweet...

Lord Valve
Glass Hustler