My 800 Garmin "can" survive a 600K without crashing or getting wierd once in a while. I have figured how to configure to have no problem doing 400K. As far as batteries, Energizer Ultimate Lithium in a Gomadic combined with a charged 800 should get me thru thru the riding portion of PBP assuming I remember to turn it off when stopped. The course is probably best parsed into three segments with Loudeac as the logical break points. I think how far you can ride before the Garmin starts misbehaving depends upon how fast you ride and the type of data that you are saving. On a recent 600K I rode with a power meter and it threw up all over itself maybe just after 400K and maybe around 14 hours into the ride.