On default power settings idle was about 98W (1400 MHz), with C6 state disabled from BIOS idle was about 117W (4000 MHz). On both cases full load on Prime95 was about 260W.
I had Turbo disabled, clocked to 4000 GHz with default voltages.
So it's not a big sin to keep C6 disabled, especially if you get some coil whine with C6 turned on.