But I think it would do a nice job behind kniferolls.  The front discs can be very aggresive and would do a nice job of sizing.

  That is about where I run mine, 8-10 inches and it does a nice job of turning it black.  A neighbor of mine pulled a 15 shank with a 9350 which I believe is right at that 325hp, but I don't think he could run it that deep and was moving a little slower.  My opinion would be another 50hp, I know I would have liked another 50hp... but doesn't everyone???

  As for the salesman saying they do pull hard, he is right!  but instead of the two and half inch twist shovels,(I forget what is on their, maybe they are three inchers?) could go with one inch twists.  Just an idea!!!

  I traded off a deere 512 ripper and a deere chisel, and I happy I did it.  Two tillage tools in one.  Never have to hook and unhook, just drive.  If it were me I would try it, could maybe always pull a shank or two off if it was to much.

  Hope I was of some help... good luck in your decision.  Oh by the way, is there any wheat in your area that you could possibly demo it on?  A neighbor of mine had some, so I actually tried it before the purchase.  Very good idea, as they are quite expensive and it was nice to see the job that it had done.