I have the 5-quart Viking, so I'll give you some feedback based on that. I chose the Viking over the KA for a few reasons:
Baker's Catalog guaranteed it for 1 year, no matter what.(Also, at that time there was free shipping)
Recommendations by Cook's Illustrated, among others.
Design, including lower height, wheels on the back, ease of maneuverability, and a lower and wider bowl. I have minimal clearance between the bottom of my cabs and the counter (old house, low ceilings).
Wattage/power
Ability to adjust the mixing attachments re: clearance to the bottom of the bowl
No unfavorable reports regarding plastic parts that are prone to breakage/wear, as in the KA. No plastic parts are used in the Viking.

I've had the Viking a little over a year and use it at least 3-4 times a week. I use it to knead bread dough (white, rye, whole wheat flour), whip egg whites, cream sugar/butter, cake batter, cookie dough, various yeast breads, heavy biscotte dough, etc. So far, she's worked like a champ. Some related info on why I chose the 5-qt. I felt the 7-qt. might be a bit of overkill for me. There are only 2 of us left at home, DH and myself. The bowl is just the right size, not too big or deep. The bowl on the 7-qt. is quite a bit deeper than on the 5-qt. and I would rather have to make 2 batches of something, if needed, rather than have a bowl that was too big when/if making smaller batches. My hunch was correct and the 5-qt. definitely is best for me, although YMMV ;o) I will tell you that I have dealt with Viking repair for their small electrics and have had excellent service from them (on the east Coast it's out of Chicago). I had the mixer for almost a year and some of the paint started to chip on the base plate, where the bowl locked in. I sent the mixer back to them and they replaced the entire base and sent the mixer back to me post-haste. The entire process, from the time I sent it out to the time I received it back, took exactly one week. Now that's expedient service!

I have this mixer. It is a workhorse and doesn't move on my mixer lift, like I have heard some complain of.

However, when we purchased it, I was told by a salesperson that Viking would be coming out with a 5 quart bowl that could be used for this mixer. I found out later that this salesperson didn't know what she was talking about.

Honestly, the bowl on this thing is HUGE and almost too big. If I had it to do over, I would get the 5 quart, even though it has a little less power.

Here is a link that might be useful:

Thanks for the responses. I'm going to put it on my wish list. I have a smaller KA--a new one would be for large batches of whole grain bread.