The 660 weights about 4 pounds (or 30%) more than the 290 with the power head and a filled larger fuel tank. That is 4 more pounds of saw to wrestle with, but... the main issue for me with the 660 was the power. A 660 has about twice the horsepower of the 290. And twice the torque. After an hour using a 660 once I was tired. It was a bear to manage in a cut for me. I lived on a sheep farm then and lifted a heck of a lot of hay bails around (2 and 3 strand bales). I was in fighting shape.
After 4 years of fairly steady chainsaw work, I found that I would use the lightest saws that I could get away with for the job. Again, in this area, the main goto saws that most loggers I know are the 440 or the 372XP. Big enough to do the job, small enough to manage all day long, day in and day out. Its a compromise. If you are a big young guy and have good stamina, then maybe the 660 is the one to get. But if you are used to running a 290, a 660 is a BIG JUMP in size, weight and power.