That is correct.
You can use one of these guys to measure power-draw

Search ebay/aliexpress for "usb voltmeter amperemeter/ammeter"
Edit: Forgot to mention, vcore of about 1.5V should get you close or slightly above 300Mhz but you'll need proper cooling, that's for sure. These guys get very hot.
Thanks for the tip on the USB meter, got one in the mail.
Which raises an interesting question (at least to me). If I have my chips clocked at 225MHz via the command line, but I have the vcore set at 1.50 via the potentiometer, how much wattage is actually being pulled? Is it the full 10.18 as referenced in vh's OP? If that is the case then what would be the advantage of keeping the vcore at 1.50 but the clock at 225MHz? Stability? Seems it would be smarter to scale back to get as close to 8.71 vcore without causing HW errors, correct?
Thanks for the patience, I just want to make sure I understand.
sidehack already answered and he should know, I guess - he designed and built them
Run them at the lowest possible vcore for given frequency that does not give you HWs.