I believe that bias setting are more related to tube life than any real significant effect on tone. When I swapped tube brands in my TSL, I adjusted the bias as it was pretty cold compared to the recommended voltage. The fattening of the tone I got was probably more due to the tube swap than the bias correction.
I think there's more to gain by swapping out your preamp tubes than tweaking bias on power amp tubes, not to say that getting your bias right isn't important, I just feel it's more about the efficiency of the electrical circuitry than it is about tone. Just speculation.