My KA Pro 600 purchased in 2001 lasted just under a year until the head worked itself loose. Still under warranty, it was exchanged for a new unit that smoked immediately upon the first startup. Got my money refunded and I now knead all my doughs manually. If I were ever to get another mixer, I'd spend less than $800 to get a real HOBART N50 5 quart mixer from ebay. Built like a tank, the N50's have a 3 speed metal transmission and are used in commercial settings nationwide.
That stated, over the years most the of reviews I've read favor the Bosch over the KA's hands down.
The older KA's built thru the very early '90's were well built, too, but the reputation of the newer ones seem very splotchy. So get either the Bosch or the Hobart which should last a lifetime.
Oh, and I've heard that for awhile back in the 90's and early 2000's, KA was bought out by Whirlpool.