I do not know what the max distance is.
What i do know is that it is not recommended to backup directly to tape over long distances. We were planning on backing up to a SL500 about 40 miles of fiber down the road but instead we decided to not go that route because it was explained to us that there would be the shoe shining effect. There are fiber switches that i know that can que the data and each end to help with the shoe shining effect but can be a little explensive.
How far are we talking about here anyways?