Hey Josh -
Your depth to bedrock, soil conditions, and your tractor are the limits to how deep you can go. I would say that 49hp isn't going to allow you to use the Bushog or Rankin at full (23") depth in heavy clay soils. The ranges I have used in the past are 30-50 hp per shank. However, your tractor is not 4WD (so traction becomes an issue) and you don't mention whether it is gas or diesel (diesel is a larger engine). I would also suggest that the following:
Tractor Supply Ripper. I have used this a number of times in heavy soil with a tractor bigger than yours and it goes through real easy. Not as deep, but works for what I needed it for. Plus its cheaper. Lots cheaper than the Rankin or BH, Good luck.
Mike Biltonen, Know Your RootsZone 5b in New York