My .02 on the alternator:
I recall reading that the extra voltage to the ignition system offsets the power loss of driving the alternator. But probably not if you are pulling high amps.

It might be interesting to have a cut out relay for the alternator output- isolate the alternator output to the ignition for the run. That would remove the bulk of the parasitic power loss. The battery can run the accessories for the duration of the run.