Definitely not a die hard Stihl buff. I've just had great luck with them in the past and its pretty much all I've ever run with the exception of my ol' ported 288, but heck that was 25 years ago. It made good power for sure. Id say between an 044 and 066 as far as power. I did however try my boss' 390 or 395 (cant remember witch) the other day and its all hopped to the max. Unbelievable power! Even more, it was lighter than my 661! I couldn't believe it! He said to me "I ran Stihl for years until I ran a 394. I Couldn't believe the difference. Ive been a Husky man ever since! Some day you will too". I know a lot if seasoned cutters that switched over from Stihl to Husky for a lot of reasons and my boss might be right sooner than he thinks! I like the power my 661 makes. However, it wouldn't make the power it does if it were stock.
I don't however like the way Stihl engineered and designed the 661. I feel its a step down from the 660 as far as being user friendly maintenance free and reliability.
Apparently right now, Husky is the 90cc saw to have for felling bigger timber.
Cut safe, stay sharp, and be aware!