Okay, slight change in what I said:
FS actually bought them for me as an anniversary
present. 
I've tried them on, and they're pretty tight. The problem is I
have relatively large feet (US 9.5) in relation to my body frame
(1.7m). I really had to gingerly slide the tights up my feet until
they got past my ankles.
Once they're on, I can really feel the muscle support. Cassie
would probably have to go for XXS, considering that I actually
bought..... XS.
No sh*t. I wanted to get S, but the uncle said that he was
wearing M in spite of having a 42-inch waist. 
i almost tot u describing a dildo
