The goal IMO of the ladder test is to find velocity/pressure nodes that give the best accuracy with slight variation of the velocity. These nodes help alleviate inaccuracy due to environmental factors or reloading variation that can affect velocity. It may or many not be at the top end. Usually there are two or three nodes present, depending on how low you start the ladder. I usually pick the case, bullet, primer, powder type, and seating depth I want to use and then vary powder charge. I choose the nodes which are evident by bullets forming "groups" and then shoot additional five shot groups to quantify/verify the accuracy of each node. Select the node you feel most confident in and meets your velocity criteria. Additional ladder testing can then be done to tweak seating depth, keeping aware of the max pressure. Hera again you are looking for the least accuracy sensitive length.

I've found I burn less powder to find a good load for a given bullet/powder combo. 300yds should work well, longer the better as distance makes the velocity variation stand out. 200yds will work, but 100yds is worthless IMO and you are better off trying three shot groups at 100. The variation just doesn't stand out.