When setting up a cross-country mountain bike, what is the ideal saddle angle to achieve optimal comfort, power output, and efficiency, and are there any specific considerations that should be taken into account when determining this angle, such as rider position, bike geometry, and personal preference? Should the saddle be level, slightly nose-up, or nose-down, and how does this impact the riders ability to maintain a comfortable and efficient position on the bike? Are there any industry standards or guidelines that provide a general framework for determining the ideal saddle angle, or is this largely a matter of personal experimentation and trial-and-error?