Pantherella Socks

Hello All:

I am in the market for a decent pair of socks - the ones I have seem to "curl" dowm the calves and the heel does not stay in place either. I have heard good things about Pantherella socks but am not sure if I should buy over the calf or long anklet. I live in the Middle East where the weather tends to be relatively warm and humid for most part of the year. I am a 7 1/2 shoe size and was wondering which size to buy in Pantherella socks since they only come in M, L etc.

Many Thanks!