What should I set my High VTEC Engagement RPM Secondary to?

This is a gray area that is kind of up to you as the car's owner. Generally its suggested to have it around 5800-6000 RPM. It can be as high as 6500 if you wish. It's not wise to set it higher than 6500 though as letting the car rev past 6500 RPM without switching to the high VTEC cam profile can cause the lost motion assembly to damage the spring retainers over time.