Imagine you are leading a project to pre-train a new encoder-decoder model for the specific task of translating complex legal documents from English to German. You are considering three different input corruption strategies for the pre-training phase: random token masking, token deletion, and text infilling. Describe the experimental methodology you would design to empirically determine which of these three strategies is most effective for your specific downstream task. Your description should include the key steps of the experiment and the evaluation metrics you would use to compare the outcomes.