I usually fire form cases with a start or medium loading and then neck size the case only. When building loads to maximum, if the case base expands .002" or more from the original fire formed case measurement, you are generally to hot. Some guys use primer flow as the answer, but I have seen primer flow in medium loadings and no flow in extreme loads. I think at the end of the day, you have to use a variety of things and make the call. Is the bolt hard to open after firing, look at the primer for flow, how much the case stretched, case damage and measure the case base.
Although most of your accurate loads are going to be close to their peak, it is very seldom that you have to go over maximum to find accuracy. If its about bragging rights, wrong hobby to get into.