Stihl MS 311 question

[Aaaaaaamakarena]

My Stihl MS 311 has a chain pitch of .325 but I see online that there are also 3/8. The questions is which is better and did I make a mistake with this one? The reason why I asked is because I'm confused with what the guy next o my lot has. His echo cs 4910 chain size is 3/8 pitch and 0.050″ gauge and he's using it for the same thing I'm planning to use

 

[Stihl 99]

Very simple conversion.
Rim sprocket, bar and chain to 0.050"
I am surprised it came with the .325" on it, every MS311 I have put together were .050"
The Farm and Ranch models from the MS291 and lower were .325", the MS311 and MS391 were generally .050"
Me personally I have .050" on all my saws so I can use the same bars, chains, sharpners, etc. I even converted my MS261 to .050"