On a scale of one to ten, exactly how bad an idea would this be?

Recently invested in some 85A BotBitz ESCs (finally!) and I'm wanting to get my entire system running to 6s LiPos so I only need one battery for the lot, naturally running 12V motors at nearly double that isn't the best idea, so I was looking at getting some 18V motors and replacing the 12v ones with those (specifically, these motors http://www.gimsonrobotics.co.uk/HRS5...r_12V-18V.html)

Would this work, and if so how many amps would this sort of setup draw during standard operation (from a battery point of view)? Thanks in advance!