I've used extensions with a motorcycle rack and have had a nearly 500 lb motorcycle on it (I was well below the rating for the truck, the hitch, and the extension, my extension is to bring it down 6" since trucks today are so dang tall). I think you'd be fine with either option. You are likely to get some slop with the extension but there are various devices to take care of that but the reducer/non-extended one is going to be simpler.