Frank,
The RPM peaks above are at peak TQ and peak HP.
*Usually*, with open headers and minimal belts, best shift is at least 500rpm past peak HP (if the engine holds together).
But, peak NET HP is somewhat below peak gross and by coincidence, that puts the best shift point near peak gross HP which is what many factory automatics did.
So in reality as Panic said, its a function of the drop to the next gear (a Powerglide will want higher shift points than a new 6speed auto), parasitic losses, and how much you want to risk your engine.
I usually Gonkulate the shift point for the best ET for my combo, then give up .1 sec or so, I'd rather be easier on the parts than get that last carlength.
As far as exhaust:
My belief is that diameter is mainly a function of how much exhaust (loosely, how much power) youre trying to send out thru it. The Lengths determine the RPMs where the exhaust will contribute to power peaks. And where to put them depends on whether youre drag, road, or oval racing. Also a function of budget, time, and ground clearance of course! Its so empirical, I think youire close already but trying different pipe lengths should be easy.
