I have a 250 watt KA and have made more bread...
with it than I care to think about.
I do have to add that my KA mixer is also about 25 or so years old, so may have been made to a higher standard, since Hobart was still producing them at the time.
I only had one instance, while making a huge batch of Nancy Silverton's Raisin Brioche dough, that I thought it was going to give up the ghost. It sounded like it was on it's last legs.
All it needed was a rest, and it has never sounded nasty since then, not even with subsequent batches of the same bread dough.
When making multiple batches of bread in a day, I did need to let the motor cool down between uses, but it always does the job.
If you think you may need a larger than 4.5 quart bowl on a regular basis, then go for the bigger machine. I rarely feel like I need a bigger mixing bowl.