Well then I think you will be disappointed with goggles then. As that's one of the problems I have with them, lot's of air flow. Which is great if your off trail riding slower but doing 90 on rail graid my eyes are usally watering. If have 3 pairs, 509's, Habervision, Yamaha. Yamaha's are probably have the least amount of air flow, not sure who makes their goggles.
Helmet can be made warm, I just used electrical tape over all the vents on the front. mouth and forehead. Then get a fog evader mask -
http://www.sledsolutions.com/store/product_info.php?cPath=164_192_210&products_id=617
Keeps out the cold and seals good.
I'am still playing with my goggles trying to tape over foam to cut down on air flow when trail riding.
You also seam to have a lot less peripheral vision with mx helmet so you have to turn your head left and right more.
No doubt helmets are lighter on your head and visor doesn't put much strain on your neck unless you tip your head back and it catch the air flow.
Hope this helps. Try and find somebody to let you try one first if you don't want to spend the money
edit: Looking in Yamaha catalog, looks like their goggles are made by Spy.
Also wanted to clarify about the 509's they are a great goggle fit helmets great, have a nose piece. I bought the polarized lenses and are great for sunny days and also cloudy days. Didn't want anyone thinking I didn't like these just because of the airflow.