I'll not open the whole can of worms, but limit my questioning to the Stihl 310 vs 290. From what I see, the two saws are pretty well identical with the exception of 0.2 HP and $30, as well as standard bar/chain offering. My inclination is to pay an extra $30 for the HP gain and longer bar/more aggressive chain. Certainly I'm no pro, just an homeowner firewood cutter, but the upgrade seems like a no brainer to me, particularly with no additional weight. Have I missed something?
Curious,
Will
If you're not going to modify your saws in any way (i.e. you care about warranty coverage), then the 310 makes sense. Hell, for $30 it might make sense, period.
But you can get a bit more out of the 290-310-390 series with a bit of muffler work, as they're pretty choked-down from the factory.
Either of those saws will be happiest with a 18" bar in terms of balance and power, based on my experience. I'd not go any longer than 20" with either saw.