I have an old Sunbeam Mixmaster that never get used, maybe a 4.5 qt. DH gave me a KA 5qt for Christmas several years ago. There are times that I wish I had one a little bigger, for double batches of cookies, SugarShacks icing, etc. It seems stepping up to a 6qt wouldn't really give me much for the $$. Would moving up to a 7qt make more sense?
You might look into restaurant supply places and step up to a 10 or 12 qt Hobart.
If I had my way I'd put a big ol' Hobart smack in the middle of my kitchen and bake my days away. I think DH may have a few things to say about that though Really I guess it just depends on how often you make cakes. Are you a hobby baker or do you sell them? I would say if you frequently have a need for large/double batches, spring for the 7qt. You'll only kick yourself if you get the 6 and then slosh stuff all over the counter.
I am a hobby baker. I have been doing cookies and cakes along for friends and church, and of course DH's office! My biggest frustration is mixing the buttercream. I have two bowls for my KA, so that helps with the big batches of cookies.
I got a new Cuisinart 7qt a few months ago and I love it! I'm a hobby baker and I made a double WASC recipe today and had tons of room still in the bowl. I bet I could have made a triple recipe with no problem (just haven't tried it yet). And the 7qt Cuisinart was about the same price as a slightly smaller KA (my DH bought it, so I don't remember how much it was). And I'd never go back to the KA now. The bowl size and shape of the Cuisinart are great, it seems much more powerful than my old KA (Artisan style) there's a lot less mess on my counter and floor because it has a "slow start" function that folds in that PS instead of exploding it all over the place . . . I could keep going. I think if you invest in one of these puppies you'll be happy you did!