We just recently purchased a fred cain ripper a few weeks ago. We had ordered a 7 shank ripper and once we got it we found it it didn't quite cover up the tractor's tracks so we order 2 more shanks and put them on so now it is currently a 9 shank. I used it for the first time last weekend and it worked great. I pulled it with a JD 5055e low gear about 1500 rpm with 4 wheel drive. We have really rocky soil and the great thing about it was it would pull big rocks up out of the soil and i could just go around with the grapple and pick them up. I measured the depth and the shanks go in the ground about 13 inches. I it really helped to loosen the soil. A great investment.
I'm not sure how 35 hp in two wheel drive would do. I would probably get a 7 shank and if it does well then buy 2 more shanks to put on it. I suppose some if it depends on the weight of your machine. The JD didn't like to pull the ripper in 2wd.