Nikon F2S w/ 28mm f/2.8 and 50mm f/1.4 or F90X with 24mm f/2.8 and 50mm f/1.8? Temperatures expected to be -5C lows and +10C highs.
My thoughts are
Pro-F2: Can still shoot it totally manual if the weather gets cold enough to render the batteries totally inoperative.
Pro-F90X: Matrix metering is way superior to the center-weighted F2 meter.
True matrix metering is superior but if you know how to work center-weighted and how to adjust for discrepancies in changes in light in your scene then it will be fine. If your batteries are dead you won't have any meter to go off of anyway so I am assuming you are familiar and fairly comfortable with sunny 16 concepts. Even with a handheld backup you will run into the same problem with the temperatures being too cold for the batteries. There is another problem. Shooting film in that cold weather can decrease the films sensitivity. I am not sure -5 is cold enough to render the film useless but it will definitely slow down the films chemical reactions. 10C should be fine. The times where it would be -5 would most likely be around 4:30 to 6am so you probably won't be doing a lot of shooting then anyway. Hopefully it will be warmer by 7-10 (10 being a stretch light-wise) and definitely should be warmer between 3-7 (3 being a stretch light-wise). Quality of light between 10 and 3 won't be much for shooting anyway. It might be too dark at 7pm but I think it is getting to a point where at least here there is still just enough to play with a little bit.
Hope this helps some. I would say go with the camera you are most comfortable with handling and the lighter rig. If it is too cold for batteries then you are pushing too cold for film and you should be adjusting exposure for the cold anyway. Also if you do shoot when it is too cold for the batteries then it won't matter if you have a superior meter (especially if the camera won't operate anyway). Dig. Kind of an even trade off so which ever one will be most comfortable to carry is the one that will be best most likely.
