Don't disagree with byeatts on the airflow, I have rp on my bikes. I mod the stock yz airbox to open it rather the 300 dollar velocity stack, but Im sure it's better. I really like the grunt off the 500, it helps jump up on the snow from a stop, it gets you out of messes. If every day was a blower pow track speed day I'd say just get the 450 flowing, but spring snow, techy climbs, ditches and creeks... I'm all for a 500 with the breathing mods as the combo.