I would suggest that your answer depends on the intended application. The 338 LM is similar to a 10mm Auto - mild to wild and everything in between.
I load 200gn moly Hornady sp at 3,400ft/s (will mark grader blade cutter bar at 200m which no other cartridge that I have fired has accomplished) using VV N165 to 300gn moly Lapua Scenar at 2,800ft/s using VV N170.
Should your question be related to accuracy, the most accurate load will depend on your rifle. Each of the loads that I have developed have been done using ladder tests for powder charge, and bullet seating depth - most have been developed for neck tension as well. Following proper load development, you are likely to be quite pleased with the accuracy potential of this cartridge. The most powerful charge is not always the most accurate.