Welcome to the world of motion control. You've got big steppers, but now what? Why did you need such powerful steppers? You say "I need speed and torque," that's a meaningless statement, every motor delivers "speed" and "torque". How much speed do you need? How much torque? What's your drivetrain? What's your payload? How fast must it move from one location to another? How distant is one location from another and what's your desired positioning resolution? All of these things are as important as the selection of the motor and the driver.
If you chucked down a few dollars, you can get a proper high-performance step/dir driver like those from Gecko: the G210 can do 7A @ 80V. http://www.geckodrive.com/g210-p-35.html