I use i4's they have never fogged up for me. I was playing in about 90 degree heat today while it was raining and there was still no fog. Beware they are somewhat small and if you have a big face they won't cover your lower jaw.
Agreed i4's there nice and comfortable and lightweight, unfortunatly i cant comment on about testihng them in hot conditions cause i live in the UK and well its always cold. but they have never steamed up on me where as others have!