I am currently using my mother's KA, 4.5 qrt, 250 watt stand mixer for making all the icing. When I make the NFSC it seems to "sound" like it's struggling. Is this normal or do I need the KA with more watt power? I will be buying one in a few months so I want one that will work well with the cookie dough, and I really don't want to break my mother's KA in the meantime... :/

I had that mixer for almost 10 years and had no problems with cookie dough. The NFSC can get hard to mix towards the end so i would add it slowly and mix.
I now have the pro 600 and am very happy so far. If you're looking to buy, it's worth looking into.

Glad to hear you like your KA 600 pro...I'm currenty looking at one of those.

I just got my very first KA Artisan and I love it. Don't know how its going to work with cookie dough yet, I'll find out tomorrow. Keep fingers crossed for me.