Best I can see around here is 11k on the west Bendigo master map, 11.5 on the east bendigo master map and 6 on the north Bendigo master. Orivate land creates a problem on each.
I can find 6.5 on Kooyoora if you map the reference area. But if you chose the correct line on Kooyoora, I am sure that you could make a longer run than any of the above in terms of time. Not much fun though.
WE could give you Kalamunda National Park to John Forrest National Park via Gooseberry Hill and Greenmount - only 15km but would most likely take you longer than the Castlemaine leg. Very steep, very rocky, very thick.
the string of maps on the eastern side of the Sugarloaf Range near Newcastle, from ODonneltown/Sugarloaf south to The Lot/Sandy Creek/Hawkemount, covers about 20km, but also includes some mapped but unused areas like the M1 motorway, the Sugarloaf escarpment, and possibly a cemetery/crematorium right on the critical path. Straight line would not be the way to do it either!
There is indeed a small gap in Chewton between the railway (northern boundary of Wattle Gully) and the road (southern boundary of Castlemaine Goldfields), though Kathy Liley pointed out at tonight's Yarra valley meeting that that is on an MTBO map.