Cathode Bias Rk Recommended Values ?

[makinrose]

After reading TUT and seeing the higher Rk values in the TUT5 projects I've begun questioning the lower more traditional values seen in Fender, Vox, Valco, and other vintage amps.  For example, I've measured the dissipation in a Fender 5E3 style deluxe to be about 45ma per 6V6 with 250 ohm resistor.  The plate minus cathode voltage is about 390 VDC so it's running the tubes much higher that 100% dissipation.  The tubes are really cooking or I am missing something?  Why did so many vintage amp have such low values for Rk? 

I've experimented with using a 470 ohm shared resistor which makes the tube set had run at about 33ma per tube. 

I'm just wonder what other people's experiences how they prefer to select the Rk value?  What values are good starting points for common power tubes?

Thanks!