I have a pair, and it's strange...I'm normally a 4.5-5. I can occassionally wear a 5.5 with boots, even a 6 but only if it's winter boots and I have two pairs of socks on. Anyway my pair of hardys is a 6.5, and it's a very high heeled sandal. It's a tad tad bit big, but somehow it still fits. No idea - Im guessing it's diff't from shoe to shoe.
First off, never fall for that "size down because the leather is soft and will stretch out" crap. I followed that advice once and ended up with a pair of shoes that I no longer wear due to the excruciating pain. The problem with PH's shoes is that I believe he modified his sizing at some point; up to about a year or two ago he used French sizing (one number size smaller that Italian sizing) and now it looks like he's shifted to Italian sizing. So it really depends on which season you're buying from. Also keep in mind that - as is often the case with many shoe-makes - the higher the heel, the more likely it is that you'll have to size up.
"Sometimes it's more important to be human, than to have good taste." - Bertolt Brecht