Back in the day's of the P45+, Phase One had a video where they showed someone take a P45+ (I know it was one of the P+ backs) out of a freezer and then turn it on, then take a picture. With the P40+ you are dealing with pretty much the same technology, (case, screen) with most likely a different controller card, CCD etc. I personally used my P45+ in conditions where the temperature was well below 32 degrees F. I believe the lowest I ever got was around 10 degrees above 0 F. The only issue you may have will be battery life as the colder conditions will sap the cells faster.
Congratulations on the P40+. I did want to ask if you looked at a IQ140 instead. I realize there is a cost difference, but the IQ screen and feature set may make the extra worth it. If you are planning on using a tech camera (which the IQ140 is an excellent fit for) the IQ screen is well worth it.
One other note, Phase historically offers their best deals in December. I have seen deals every year around the 10th of the month. There is no idea on what product set that Phase will give a extra incentive on and this year they may not but in past years December has always been when deals come out.
Hopefully you are working with a dealer and they can get you a demo of the IQ140 also.
Paul Caldwell