I need a new GPS unit that will allow me to set a 'virtual partner' at a pre defined speed and have it tell me how far ahead or behind of it I am in real time. The purpose is for a 340ish mile ride that I want to finish in under 24 hours. Since i know the total distance and time I want to finish in I will just divide the distance over 24 hours and set that as my goal average speed. It is an ideal way for me to motivate myself to keep the pace I want for the ride when I am tired in the middle of the night and want to give up.

The Garmin Edge 810 was supposed to have this feature but everything I am reading online is saying it doesn't work well for long rides, if it works at all. I have a dynamo hub so being able to charge the unit via dynamo would be great but not required.

Any other options out there for me? I also want it to track me and save my route with time but any GPS should do that.