I have several of those "big Pro saws" including Husqvarna 268xp, 272xp, 372xp, Stihl 066. When it comes to cutting firewood, I always reach for a smaller, LIGHTER saw. Its MUCH less tiring to carry and repeatedly lift the smaller saws.
A couple of weeks back I was out milling a 36" oak log. I took 2 saws. The 066 with 36" bar was on the mill, and the 346xp(50cc new edition). I did the trimming of knots and bark with the 346, AND when I needed to cut a 24" length from the center to setup the mill, I used the 346 as well. The bar was BURIED, and it just kept cuttin'.
I'm running 18" 3/8 .050, and am really impressed as to how well this saw cuts.
The MS361 isn't much heavier, and will have more power than the 346xp. The 372xp is heavier still, and will again have more power.
Don't go overboard on saw size, weight, and bar length. He might over do it, and that wouldn't be good. It not just the saw, its the size and weight of the wood to be moved as well.