We have an 18 foot turbo-max.  It is also recommended 10 hp per foot.  We have been pulling it with a JD 4960 (215 hp).  We also have a JD 4850 (210 hp).  You can honestly tell a difference pulling the turbo max with each tractor.  The speed recommended is 7-10 mph.  By having the extra hp we can hit 10mph easily on our river bottom ground.  In our hilly ground we end up running closer to 7.  I would guess it depends on the type of ground you farm (flat or hilly) if you tractor could do it.  I would recommend from my experience to have more than 10 hp per foot.

Corn on corn