Square pico can be fun for a minute but saws that would normally run pico can have trouble pulling it.
On the other end once you move up in size to a saw that can pull it with authority, the chips don't clear as well as they would with a bigger cutter frame.
It can be a real guessing game if the square pico will actually be faster with any given saw.
What pulls well on a ported MS260 might too much for an unported saw and not clear well enough for a ported 346XP to run at its best either.
I have ridden this rodeo and for most ported saws I like 3/8 better than pico.
Mike (@canadianfarmboy) made a really sweet .325 to run on his ported 036, but honestly I havent run much square .325 as it is not common in this neck of the woods except on the MS290.