This should help.
7th one down is a Pro 600.

Here is a link that might be useful: Butter

I've made butter with niece... during a girls' weekend. Have a "vintage" KA stand mixr that I found at GOOWILL for $19.99... crank up/down bowls, had whisk, paddle and dough hook. Even found a SPARE bowl a few weeks later! I use whisk on about medium. Once you've gone PAST whipped cream, I'd slow it down a touch. When the whey starts to come out of the fat... can be a bit sloshy.