In reply to Cora:
If you are normally a 37.5 in Leathers than you are most likely going to be a 38 or 38.5 in phantom 8000 or Olympus Mons. Double boots come up differently than singles in sizing.
I would recommend to go and get your foot measured (while standing) and as a starting point go up 2 euro sizes. I know people that have gone up 1 size bigger than the foot measures BUT most people I know have gone up 2 sizes. as I said it is a starting point not a rule.
If the Spantik dose come in a 38 you could always buy the liner for a Spantik and put it in the Olympus Mons to help the fit. After all they are the same liner.
Cheers Poo