What are the key factors to consider when setting up a pain cave for optimal Zwift racing performance, and how do these vary depending on individual rider preferences and physical characteristics, such as height, flexibility, and core strength, particularly in terms of bike positioning, cleat adjustment, and ergonomics, and are there any specific guidelines or recommendations for configuring Zwifts display and data visualization to maximize focus and minimize distractions, or is this largely a matter of personal experimentation and trial-and-error, and how can riders balance the need for immersive visual feedback with the importance of monitoring critical performance metrics, such as power output, heart rate, and cadence.