I've had Heavy Duty KA Mixer for 17 years but want one with a bigger capacity and stronger motor. I am looking at the KS Professional 600 series. I mostly do cakes, icings, cookies, but also want it strong enough for occassional bread doughs. Anyone know about the KAPro 600 series? Is the gear box still plastic or are they all metal now? And also, is it noisier than your average mixer? Should I even consider buying a factory refurbished one?