Interesting, I prefer 250 myself for most wing guns, with a few exceptions. I like the firepower at closer ranges.
Note regarding the 50s. This, imho, is the cause of many of the complaints of the 50 caliber in AH: Guys setting conv to 400+ and then complaining of lack of firepower. I have no proof, but its a hunch.
Its true the farther convs are easier for shooting at a running con, say out to 600-800, but you will pay a price closer in.
In the end, hey, if it works for you dont change it. We all have our own ways.