This gets covered a lot here and other places. Be a little careful of making definitive statements until you try it. People will read it and get a little panicked and then email me.
Use watts, look at the pololu conversions for the drivers. Yes the steppers chop. That is why your steppers can be over powered by a lot. They aren’t always driving full power and never should heat all the way up. The 80C is a max temp you should never let them get that hot. When you adjust the voltage at the pot tin turn controls the total wattage.
You can easily drive 2-4 of these big steppers on an activity cooled 8825. There are hundreds of these out there Using this exact setup. And if you need proof I ran all 4 of the extruder steppers in parallel, http://www.vicious1.com/4-head/