Amplifier Efficiency

US Amps claims:
86% @ 4 ohm
84% @ 2 ohm
76% @ 1 ohm

Sundown claims:
84% @ 4 ohm
81% @ 2 ohm
64% @ 1 ohm

DD M3 claims:
>85% @ 14V

RD D5 claims:
86% @ 4 ohm


How do real world efficiencies stack up to manufacturer ratings?

Example:
I'm running 2 AP15001D's @ 2 ohm, for ~900wRMS each. That's:
1800 output power / 83% efficiency = 2170 input power
2170 watts / 14 volts = 155 amps of current input

If I've got a 190 amp alternator and some battery support, I shouldn't see much (if any) battery drain. Does this mean I can expect somewhere between 12.8 and 14.7 V throughout my streetbeat runs?

Yes, and that under heavy load (burps or low continuous notes). Music has much higher crest factor than a single frequency tone.