"Wouldn't the (common extensor and flexor tension) differ a bit depending on supination/pronation of the forearm and extension/flexion of the wrist though? In most puching these come into play as well don't they?"
Yes. In supination, they are more lax than in pronation. However, both are more lax in elbow flexion than extension. So by using the 'If A>B>C, then A>C' philosophy, elbow extension with pronation is the most tight while elbow flexion with supination is the most lax.
With that in mind, my punches start high in the chamber with elbow flexion and supination and the pronation does not occur until just before impact when the elbow is fully extended.
"Hmmm...I figured they didn't play the same major role as biceps or brachialis, but I didn't think their colelctive effect on flexion of the elbow was that minor, though it make sense I suppose."
The little effect is due to the small lever arm and the relatively small mass of muscle compared to the others mentioned.
"It still leads me to believe that for most folks the answer (and seemingly MA experience has backed this up) is that yes, you will be a bit slower if your fist is super tightly clenched prior to punching, perhaps not because of this specifically, maybe it is a sympathetic thing with tension elsewhere."
Yes, the reason most people have any negative effect from a tight fist is due to the overflow of tightening into other muscles. The little effect the common flexors and extensors could have is minimized further if the punch turns over at the last minute.
In fact, try this. Make a tight fist and chamber it high. Snap your hips and let the punch fly with NO purposefull shoulder flexion or elbow pronation. It will be a little less than controlled, but you will feel a very fast punch with an automatic pronation at the very end of elbow extension. It is how the joint moves when allowed to move on its own.
"Anyway I wasn't trying to do anything weird with jargon or anything, my assumption was there are plenty of people on here with the background to know exactly what i'm talking about and roll with it, and maybe explain some stuff to me."
You may be right
"I don't think i'm offending anyone here by talking about it, there are certainly less productive threads! "
You are certainly right there!