Why not just buy one of the new NEMA17's from MakerFarm and not worry about it. It's only 15.00 and that should solve any worry about heat. Get one for your extruder too. I bought my 10"kit at the end of August and the motors it came with, even with a 6 hr print, the extruder motor never gets above 38c measured with an infrared gun. Just mildly warm to the touch. Seems like a cheap but worthwhile purchase.