Quick update. After being frustrated by the box blade getting hung up on weenie little stumps, I went back over them with a $160 TractorSupply subsoiler and it was like night and day! Just line 'er up, drop the 3pt about 2' back and let it rip...literally. If the tractor stops moving forward, just tug up the 3pt and inch forward at the same time. Probably grind a edge into the front of the subsoiler to cut the bigger roots. Didn't try on anything over 4", but you could probably pull 2 a minute with the thing if they are close to each other.