To get a taste of what it is like to truly live with a big pro camera over an extended period of time, which would help me decide whether to adjust my financial priorities toward a 1D X, I recently acquired a quite gently-treated, pre-owned 1D Mark II N. I could not find one scuff or scratch on it! Thus far, I am liking it, with the additional weight not being an excessive burden, though the true test will be an all-day walk-about, when I can find the time. I do think the weight helps stabilize the camera when shooting hand-held, at least for short periods, before fatigue has a chance to occur.
Another motivation was that we are having a wet winter in SE Texas; the 1D cameras have superior weather-sealing.
When I could not format an 8GB SDHC card, nor a 4GB, I did some on-line searching, and learned the camera needed a firmware update. This was a challenge, as the procedure differed a bit from my updating my 7D camera, but I finally accomplished the task. (Apparently, in 2005, when the 1D II N was released, 2GB was quite normal capacity for an SD card, though CF cards of larger capacity existed.) Now, when shooting evidentiary images, I have instant back-up, with both CF and SD cards.
AF performance is quite good, though I have much to learn before I can truly say much about it.
Noise is a problem at high ISO, as expected with 2005 technology in a cropped-frame came. 3200 looks terrible, far worse than a 5D1 at 3200. The 5D1 is also 2005 technology, but it has a full-frame sensor. The 1D Marks I through IV have the APS-H sensor, with a 1.3x crop factor.
If Karl Grobl can tote a pair of big pro cameras, on straps, I reckon I can tote one. He carried two 1D Mark II Canons from 2005 until quite recently, then went back to Nikon, with a pair of D3s cameras. His images, shot with the earlier 1D Mark II cameras, are partly what prompted me to try a 1D Mak II N.
Life is good!