I used to get around 70%, but ever since I started mashing with 1 less gallon and using that to rinse the grains, I've gone up to over 80% consistently.
I second this approach, both for efficiency, and ease of process. The sparge step can be used as a volume adjustment to reach intended pre boil volume. This allows you to rough in your strike water amount, and fine tune with the sparge step.
Very simple and effective, just the way I prefer!