It's good that you're planning on doing this over 4 days and driving down. Since you're driving, you may miss out on some great rides over Monarch Pass, and the Million Dollar Highway (I didn't get to ride the Million in 2013 due to time constraints). Otherwise, that is a reasonable amount of time for a trip like this as you can get there driving at a moderate rate, stop and take pics, and have a buffer in case of break-downs and emergencies. Fair warning, in May, 2013 the area around the spine was pretty warm, so plan on it being hot.