You can get a Stihl 261, their smallest pro saw at 50cc, for about $575. The prices go up from there. The 261 can handle an 18" bar with authority in hardwood, and pull a 20" fine in soft wood. Next would be the 362 (60cc, 20-25" bars) then 441 (70cc, 20-28" bars). Beyond that you're talking over a grand for bigger Stihls and getting into some heavy powerheads. For the record, I have a Stihl 261 and a 461. Of all the saws I have run over the years, the 261 is my favorite saw by far.
For what you mention, I'd suggest a semi-chisel chain, which has a rounded corner on the cutters. It is much more robust under "working" conditions or when cutting dirty wood or fence posts (treated wood). Full chisel chain, with square corners, cuts faster but will dull in a heartbeat if the wood isn't clean.
Stihl makes a green chain with anti-kickback features, and yellow chain without. The only difference comes when plunge or bore cutting with the tip of the bar. If you never do that, you'll never notice the difference between green and yellow. I run green most of the time, but have a couple yellows I rotate into the mix now and then. For what you describe, may as well run green and get a little extra safety.
The green semi-chisel will be the Stihl "RM3" chain. If you go yellow, its just "RM".