I cant say which one would be best for you. But here are a few things to consider.
The grading scraper will pull every bit as hard as a blade the same width. In some conditions harder. You have two blades, not one, both cutting and they are both always full and pulling under a box full of material if it is working right.
The 822 lb 7' scraper gives you 117 lbs per foot of blade which is better than the 6 footer at 600 lbs which gives 100 lbs per foot. The more wt per foot the better. I have heard some say that 150 lbs per foot is good. I have a 5 footer that weight 575 lbs and some times I add 100 lbs to it. But I have no rippers and some very hard packed gravel.