Re GPS choice - I took an eTrex 20 this year and it worked out pretty well - batteries would last around 2 to 3 days per set. I loaded free Topo maps (from gpsfiledepot) for each state onto a memory card and just switched maps when I came to the state boundaries. I also loaded Scott's 10000 point TD route file including the 2012 route changes and it worked superbly.
One gotcha that caught me out at the end of a very long day was the colour schemes. I had my eTrex set to use the same scheme for day and night, and the pink route didn't show up very well over an orange road. Having emerged from the forest late at night with just a gentle roll down the hill into Cuba, I ended up going 7 miles in completely the wrong direction before I realised I was following just an orange line and not a pink one. I could've cried when I realised! Apart from that, I don't think you can go wrong with an eTrex.
One last thing - make sure you tie the unit to your handlebars using some nylon string (or stronger) - there's a small metal loop on the battery cover. I had to grease (with lip balm) the rails of the mount to enable me to get the unit out easily for battery changes - mainly due to gradually weakening fingers as a result of hand nerve damage. Although the unit was always well clicked in after such changes, it still flew out of the mounting at least 5 or 6 times during the race - without the tether I'm pretty sure I would have lost it.