Is that your best case scenario
Minus nuclear winter?
I would have thought reduction of sunlight would be enough in the northern hemisphere to wipe out plant life- livestock food resulting in death of whatever survived the radiation levels. In other words not only radiation levels on contaminated surfaces affecting ability to grow food for human consumption but livestock aswell ontop of the lack of sunlight through a nuclear winter. If a nuclear winter only lasted 6 months you would think the devastating effects from loss of ability to grow feed and food would =9 months minimum before plant life would have a chance to start recovering by which time livestock has died from natural causes,humans trying to survive, lack of safe food and water.
There is some educated guesswork involved in this scenario, yes. Some areas will get hit harder than others; some areas will barely be affected at all, except for loss of modern conveniences. The scale of the exchange will have a huge impact on survivability. How many missiles and warheads get intercepted? How many malfunction and don't detonate? How many miss their targets? Weather conditions at individual impact points will greatly influence thermal pulse effects and any fallout. The sheer number of these variables make it almost impossible to predict on a global scale with any accuracy, even with modern computer simulations.
Nuclear Winter was a theory proposed in the 1970s by well-meaning scientists such as Carl Sagan, a man who I greatly admired. However, their theory has largely been debunked for two reasons:
1: The computers they were using to model their simulations of climate change after a nuclear exchange were primitive, at best, and couldn't possibly take into account all the variables I mentioned above.
2: The nuclear weapons that were actively deployed in the 1970s are no longer deployed today, specifically the "city buster" warheads in the 5 megaton range or higher. The damage caused by these multimegaton weapons is what they used for data in their computer simulations. 21st century warhead yields are much, much smaller than when the Nuclear Winter theory was proposed and that reduces the amount of debris thrown into the atmosphere by explosions on an exponential scale. Ergo, the results of their simulations are no longer accurate.
Could there be localized climate impacts that affect the ability to grow crops in the short-term? Yes, that is absolutely possible. But analysts mostly agree that it won't be the global catastrophe predicted by Sagan et al.
Am I guilty of some optimism here? Perhaps. But I would rather prepare for the best-case scenario and be wrong than not prepare at all and be wrong. My wife and I have last-resort plans if we determine that a nuclear war is not survivable. This should be a part of everyone's preps, just in case.
. And from the look of people's preps ,I can see why 
.