I have several 50cc saws. I like a 16” bar on all of them, but usually if I’m cutting something 16” in diameter regularly I’m not using a 50cc saw. That is to say, the bar isn’t frequently buried.
In NY, while blessed with lots of hardwood, I use the 50cc for thinning out pine, hackberry, sumac, wild grapevine and brush, as well as delimbing felled and fallen hardwood trees. If the saw is going to see a lot of small stuff, I use .325 x 0.050. I don’t worry about narrow kerf, although the new Husky SP33 chain I believe is a narrow kerf, but .325 tends to get caught less and throw a chain. Also, if the engine is right at 50cc and built for speed over torque, it’s easier to pull the smaller cutters. The .050 has less rotating mass since the cutters are thinner, and it makes the saw feel snappier revving it up. If I’m going to be cutting larger stuff 6-8” or more frequently, especially if the power head has low-end grunt, I have it setup for 3/8 x .058. The .058 clears chips better in the bar rails, and the 3/8 is smoother cutting than .325. In either case it’s a 7-pin rim sprocket.
If the wood is frequently 10-12”+, I’m going with a 60cc powerhead.