I would really ask yourself what is it you really need from a camera. The 1d has great battery life, two memory slots, weather sealing,multi spot metering , heck way better over all metering than the 5d mkII. Now the 5d the center point focus point is golden, has great resolution and color, high ISO beats the1d by a stop. If you know how to use a histogram you can easily over come the 5 d's metering btw. The 5d has a far superior LCD , the mkIII's doesn't come close.
I find myself carrying my 5 dII the most, but when the shooting pace is fast with little time for adjustments I like my mk III better.
It's all about your shooting needs