I have been using a scott turbo with blue color changing lens for many years, never had a problem rarely fogged up on me but age has gotten to them, was sooo exited to give my local 509 company a try I even have friends that work there, got me a pair of 509 x5 no more than 30 minutes into the day I was fogged up like crazy, tossed them into the backpack pulled out a cheap pair of STAGE promos from another thread, I was so impressed I'm buying another with different color lens, spent the rest of the day in that goggle and not a spec of fog... I will give my x5 another try next time im out, this time I will take off the nose piece I suspect that is the culprit of trapped hot air going up into the goggle.
Its funny and my wife called me out on it too, I spend so much more $ on gear for my other winter passion, snowboarding, just spent $250 on a pair of smiths , but for snowmobiling I tend to cheap out.