I got the Fred Cain 9 shank field cultivator and it was just right. Pulled up rocks without choking or breaking, dug in at least a good foot, left some half decent furrows (not that I'm qualified to judge), dug up all those infernal concord grape roots, though I'm wondering now many of the chopped up pieces will try to grow again, hopefully a little baking in the sun will deter that and I'm carting away what I can. Anyway, it was just what the doctor ordered for my situation (previously worked New England soil, but not for some decades).