Motownhound, I base my leader lengths for dipsys off 2 things:
1: length of rod used
2: length of boat used
I run Shimano talora dipsy rods that are 10 foot long and I only fish off a 16.5 foot boat, so in turn I try to keep my leaders no more than 9 foot. This gives me some room to 0ull the fish up and also I can move towards the front of the boat(open bow) to land a hard fighting fish. If you are running say an 8'6" rod, then I would personally stuck with the 6-7 foot leader. Some of my work harnesses are only 5 foot long off the dipsys and they produce a lot of fish for me! Best of luck to you on this season!