The TDP limit can be turned on or off via bios (not user controlled setting on GB), intel has made that clear from the start. I posted earlier in this thread or the Gig thread a pic of one mobo bios allowing the user to turn TDP on or off as well as set core limits, think it was an engineering board.

Everest reads Wattage from cpu, max specs is 130W TDP. You can OC the cpu on high vcore, turn off thermal throttling in bios (so that mech doesnt throttle it), and run coredamage at 100C and 150W and turbo will still be engaged on all F4 and after bioses. So like Reverend said, turbo on GB boards on F4 and newer bioses = 21 multi for i920 and 23 multi for i940.

Regarding it requiring less voltage for 21 (turbo) multi on i920 than 20 multi given same mhz, that is no different than my i940 requiring much less (6-7 notches) vcore using 21 multi (turbo off) as opposed to 22 multi (turbo off as well) for same mhz. For whatever reason i940 23 (turbo) and 21 (nonturbo) requires much less vcore than 22 multi. And many i920 require less vcore with 19 and 21 multi than 20.