I'm thinking...something in the 420mm-450mm range. I have 180/300 that will work on the 5x7 and 105/125/210 that will work on the 4x5. I'd like something even a little longer for 5x7 *I think*, but I have yet to try out the 300mm yet to see what I think. It's huge and I have to mess with the current board or make a new one.