does speaker impedance effect bias setting?

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My hunch is that the Fender '6L6' based output stage operating conditions used throughout the BF and early/mid SF era was originally designed around the 5881 in the 5Fx range.
Of course the 6L6GC become the preferred type when it came online, but as that has the same characteristics, there's no need to increases the conduction angle / idle current above that which would be suitable for a 5881's 23 watt plate.

Then again, there are twp totally different 'crossover notches'.

I set bias to remove the small signal, just out of Class B distortion.

Then (I do not go here) there is the 'just before max power' kink.

Yes, the big issue with the crossover notch method is the gm doubling effect in AB amps http://music-electronics-forum.com/t41210/
By the time the idle current is increased sufficiently to remove the error gm doubling introduces, the amp will likely be running close to class A.

[Tone Meister]

Hey guys thanks for the response. My bias setting was 44.7mA? 6l6gc =30 watts so 30*.7/470 (plate voltage) = 44.7mA. Am I getting the math wrong somewhere? should I be closer to 35?

Your math is fine if you believe that 70% "rule." You'll find many of us MEFsters don't subscribe to it. Of course you can listen to the amp at both - or any other - bias setting, find if you can tell the difference. Most sensible folks want to keep the heat down, get some more life out of the output tubes. I can only guess the 70% crowd have no scopes and don't trust their ears, they choose to run the bias unnecessarily high just to make sure they're out of the crossover distortion zone.

Without consideration to cathode biased amps, the only amps [power tube types] I've ever liked biased anywhere near 70% happened to be Marshalls - a 2204 with 6550s and my JTM45 build with KT66. Otherwise, using the scope, a CompuBias, and mainly my ears, every Fender I have ever owned or worked on ended up between 48% and 62%, with an estimated 90+ percent of those right around 52-55% which gave the best tone to my ears, and equally as important, the best feel when playing at show volumes. I calculate dissipation to document a reference point, not because a particular bias number was the intended target from the start.

Since the late-70s, I've owned and toured scores of different amps with just about every popular power tube type, and almost without exception, once PT dissipation exceeds 65% I can hear and feel artifacts I don't care for, the 6550/KT88 and KT66 being the exceptions. Of course cathode biased amps typically run at 100% and more and aren't part of this discussion.

That plate voltage is pretty high. What model Super reverb and what rectifier does the schematic call for and what rectifier do you have in there now?

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This is an AA763 Blackface Super Reverb. The schematic: http://ampwares.com/schematics/super_reverb_aa763.pdf shows 460v on the plates with a GZ34 rectifier tube.

[Tone Meister]

The 10-volt increase is certainly reasonable then. When dealing with the vintage amps, I tend to rely on the filament voltage to assess when the voltages are in check, or not.
That said, have you experimented with different bias points? How does it sound and feel?

It should be clearly noted that I am NOT a tech, but a pro player who dabbles with this stuff in his spare time - but I did stay at a Holiday Inn Express last week. This forum is chock full of real pros, which includes most everyone who posted in the thread, except me.