Starter motor lugs it is.
I like your setup Mark but I think the Sav has a bit more panel space than the 701. I don't want to lose any legroom so won't put anything below it.
Today I pulled the positive cable through to the battery, measured length and cut it. Works out to 2.28m which I'm fairly happy with, I was afraid it would go over 3m. I also drilled out the rivets at the front of the pilot's seat, will need to lift and get below that to fix cable holders etc, and also to join up the isolator switch.
On the negative side, (not "bad", just negative!) - I put in another gland through the firewall and ran a short section of 14mm2 from the starter motor lug through the firewall and to the back of one of the bolts holding the regulator on. Will mount the negative bus bar close to that, and also run 14mm2 from that bolt alongside the positive cable until under the pilot seat, where it'll terminate at the isolator switch. Then from other switch terminal to the negative terminal of the battery. I believe that should give a nice solid earth return - happy to take on board any suggestions though!
As far as running the cables along the cabin floor under the rudder cable - have others run anything to protect them (eg a cover of some sort) or just left them exposed? Thinking a "top hat" section length of aluminium riveted to the floor may not be a bad idea.