When I got my 6 quart (Professional 600) KA a few years ago, it only took me one batch of bread...
...to break it. It overheated and oil oozed out around the spindle and dripped into the dough. I took it back to Macy's and they exchanged it.
So far, this one is holding up.
I have noticed that with the spiral dough hook, it takes at least 1/3 more kneading time to properly knead the dough.
Ugh. If Breville makes a 6 quart, I'm giving it a try.
Michael