This is all really good info, and the starting procedure for a Stihl is spot on, works everytime for mine.
However, compression on a chainsaw is 150-180psi new, so 120 is barely acceptable, and anything less than 100 is considered worn out. My 20 year old Stihl 046 Magnum still has 155psi compression, and my 6 year old MS361 is still at 180psi.
Craigslist is another good place to find them, but the good deals go really fast. You can't go wrong with a Stihl or Husky, but don't rule out Jonsered, Dolmar, Makita, Tanaka, Efco, John Deere, and Redmax. Jonsered is basically a Husky, and Makita's are rebadged Dolmar which are excellent saws. If you need info on a specific saw, Arboristsite.com has a ton of first hand user opinions in the forum, or feel free to shoot me a PM for my number and I'll be glad to share what I know (which isn't much compared to some guys).