personally I would go old school, use one of the big chainsaw motors with some serious grunt lets see a Homelite super XL around 58cc
I know of a Pioneer 600 I could pick up for $25 that is complete with spark but not running that is 103cc there are plenty of old macks as well & lets not forget the sachs dalmers. the macks go up to 125cc & with racing gocart parts & stroker crank you can get aprox 150cc but you can find inexpensive 80cc saws cheaply
there are plenty of saws with some serious grunt in the 60cc to 80cc class & there are quite a few saws over 100cc
there are guys that race chainsaws & with right fuel turn 25,000 or so RPM but thats in more modern saws. but look at the old saws they turn 6,000 to 8,000 rpm but when you crank them they rumble with power.
by the way I have like 20 chainsaws & for big wood I always pick up one of my old saws. but for medium sized wood or just firewood I will pick a lightweight saw for what seems best for the occasion.