No worries, I have just reviewed some shots I took using a simple two studio flash set up (interfit) with a Kenko IR transmitter, I shot these using a 7D I managed to shoot at 1/250th at F8 with no sign of sync banding. The 7D has a max sync of 1/250th so I would have though you should get faster speeds than you are getting!
Here is one of them, this I believe was shot at F9 @1/250th ISO100
