I would always leave the reference consumption Wh/Mi @ 65 unless I knew my consumption was going to be a lot higher (head winds, really cold weather, snow/rain).
I would change the reference speed % like the OP was doing to approximately what I would be traveling. This is the % that is multiplied by the speed limit to gauge your own speed reference. It doesn't help to use only 105% if you are not expecting to go only 5% over. Use the percent to get close to your planned speed and it will calculate your consumption accordingly.
Max speed I think is only useful if the speed limit is higher than your planned speeds across the route, so you don't want it thinking you will be going faster than you really will as it calculates the plan.
ABRP goes a good job finding the most efficient routing, vs. the Tesla nav or even Waze trying to find the fastest route. It also factors in the elevation changes pretty well.
If you run it on the Tesla browser during the trip, it will continue to update the planned vs. actual. So far, I've gotten it to work out pretty close and if anything, ABRP tends to be slightly conservative.