Trek has some new computers coming out soon: wireless with a large display. These aren't cheap ($80-$140( but the prices/features appear competitive with the other higher end computers. The transmitters are sold ($54) separately because there are different ones. One of the transmitters is a dual one that does cadance/speed from the chainstay.
I asked the sales rep about the long ride issues (distance/time) and he looked at me funny! Maybe, they won't have the limitations the other computers do.
It looks like trip time is 99:99 hh:mm and trip distance is 999.9 mi/km