The little ATV trailer with a quad on it is pretty light... but consider the lever effect of a hitch extension multiplies your otherwise low tongue weight (which I estimate at maybe 300 lbs) to more like 1200. So you're right -- unhook the trailer and you're closer to your proper weight. BUT, that means not towing. I would not want to risk going that far over on my tire ratings; that's one place you don't want to mess around. The last thing you want or need is a blow-out because of it, especially at freeway speeds.
But, it's your stuff... if you want to risk it, that's up to you. BTW if you do have a blowout and it causes an accident, the cops WILL look at that sort of thing.