Well, you folks have covered all the angles, but I'd like to re-emphasize 1 from a prior post. The 20" blade saws are heavy, and the vibration when going through a large piece of hard wood (not pine) is considerable. My wife (125 lbs) would not last long. Indeed, most males, who don't saw daily, won't get past an hour or 2 with a large saw (yeah, they're still standing, but arm reserve strength is too low for safety - i.e., stopping a "kickback"). After the hurricane Hugo hit the South Carolina coast in 1989, there were a lot of folks buying chain saws and trying to clear out their yards - the acute injuries were common, but the chronic stuff such as elbow and shoulder tendinitis was epidemic, and lots of inexperienced folks still have golf, tennis or other game problems because of what they did to their joints over that 5-7 day period of post-storm clean-up. So, keep in mind what you hope to accomplish, over what time frame, and your arm strength and body mass.
Oh yeah, Sears has an 18" Husqvarna on sale, now.