hey Nathan,
You network setup would be good. Is your computer doing anything when you are trying to play the file on the PS3? try shutting down all your computers and just have the PS3 and nas working, see if that makes a difference.
From what you described i am running the same devices, ps3(wireless), laptop(wireless) and have a Linksys WRVS4400N and i have no problems. My network is gigabit router and switch with cat5e cables and wireless N if supported by the device. I am running the same f/w and rev B as well so there is not reasons for it to be choppy at all.