If you have the money and want one, get it. However a 660 or 661 is the new model, is a heavy pig. You don't need giant falling dogs, and I would assume you don't need a full wrap. I would look at a 441 or 461 (I'm not up on the new model numbers). You can get them without a full wrap, they don't have giant falling dogs, and they weigh like 2-3 lbs less. The smaller saws are rated by stihl for 32" bars, so if you had to you can run bigger.
I have an ms390, its not a pro series saw, but it runs good. I have a 25" bar on it and it rips through wood with it. I still use a stihl 211 for limbing and smaller stuff. I got a husky with a 20" bar this year to try too. The bigger saw will just wear out your arms doing bunches of light work with it.
Edit: my saw is a 311 not a 390.