Yeah....right!
I take a UK 4.5/5 - have been wearing stilettos for over 20 years - and still have trouble with 6" heels.
Personally - I don't believe anyone who says they can wear them comfortably all day.
Even the models, dancers and other 'professional wearers' I know can't last all day in 6" or more without platforms - they're just too hard on the joints and muscles.
A UK Size 3 foot is 23 cms in length. A 6 inch heel is 15 or 16 cms high.
So - you can walk around all day with the heel and sole of your foot at an 82.5 degree angle - just 7.5 degrees off vertical??