OK here's my $0.02:
1) I cannot speak about Arai or Shoei - but my new AC-12 barely fogged yesterday while I was out for 30 minutes in 28 degree weather.

2) Advice for a fogging shield: I used to wear an Itech (which is more or less the same as a visor on a moto helmet) on my hockey helmet. Before each game I would put a small amount of hair shampoo on the inside of the Itech and spread it around the entire surface. After the shampoo has covered every inch of the mask, I would just wipe it off with a towel. Never had any problems with it fogging during a game (or practice). Don't ask why or how it works - it just does. Maybe it will work in this situation too.

 

thanks for all the info. Looks like one of those things I'm just gonna have to live with.