I have a 661 full comp - my bonce is 57cm, but the 56-58 didn't fit, too small. I went for the 58-60, which fits perfectly, although we measure dmy mate at a 58 and he said the 56-58 fitted him perfectly... I have a wierd head I think.
Anyway just spent a week in morzine with it, its white, light and very tasty. Keeps your head cool. I had a few wipe outs and was glad of a full face.
If you are interested I have the brand new in box 56-58 which I didnt get round to sending back to chain reaction and its past the 30 days now so I need to sell.