My 650 bogs down too. Its 85cc. Dont get me wrong it does a good job at cutting and everything, I just wouldnt recommend anything smaller than a 460. And if all your doing is cutting firewood, then you shouldnt need a 28" bar anyway. A 20" - 24" would do just fine for that. In order to get a saw with a 28" bar that will still cut good your talking $700 or more. I paid like $900 or something for my big saw and thats just stock.
Well, when you are falling stems that exceed 4' dbh... I only run into stuff that big occasionally but when I do I don't like borrowing equipment. Kinda hard to fall or buck stuff when the bar doesn't reach going from both sides. That is why I have a 28". Normally the 361 carries a 25".
Harry K