I'd leave the back checkers alone, as it doesnt feel safe to split against those two big stack on the 8-point and 6-point.
Plays that hit loose look really bad too.
So that leaves us to play either '13/6' or '13/7 8/7'
'13/6' unstacks the 13-point but stacks the 6-point. It does one good thing and one equally bad thing. The plays does nothing, it's basically a waiting move.
'13/7 8/7' unstacks the 13-point and it builds a keypoint. In return it gives our opponent a shot on our 8-point. So it does two good things (unstacking, making a keypoint) and one bad thing (leaving a shot), that looks like a good trade off to me, so that's the play I would make '13/7 8/7'
I keep going back and forth between 24/18 24/23, and 13/7 8/7. I am leaning toward splitting the back checkers, but don't have a big preference. After work, I'm going to see what GNUBG says about the possibilities.