I'm very short sighted and don't get on with contacts so it's always been glasses for me.My current helmet (Givi) has grooves that are about half an inch above where my spec's arms go. Thought I'd have to do some surgery on the padding, but it's not been a problem as the specs seem to be making their own groove.As for misting up, it's usually OK when I leave in the morning 'cos I hold them over a gas ring until they're bearably hot and, being glass, they hold onto the warmth long enough to get me through the initial slow bit.The problem comes when you have to go slowly of course. Breath-holding can help, blowing downwards ought to, but I've never had much success with that and a lot of water condenses onto my cold chin too. I've often thought of fitting a mouth tube to direct exhaled breath to the back of the helmet. It'd also offer the option, should some car driver irritate you, of pulling ahead and blowing a gobful of saliva onto their windscreen.
Have worn glasses for most of my adult life-I use a pair of rimless lenses in a very thin metal frame that gives good peripheral vision. I wear a Shoei Neotec with Pinlock insert-& the only real misting problem occurs under conditions of really cold but wet conditions-get round this by opening visor very slightly.Legally you should cover yourself as there is a code on driving licence stating "glasses to be worn"-there are insurance implications here also-dont risk it!
Anyway I may not be able to read that numberplate from 100 yards away but as long as I can see the bludy car it's attached to then I'm alright haha