I just bought my Clarity last week, so I don't have a ton of experience with it yet and none in cold weather. Living in Wisconsin, I will find out about cold weather range in a few weeks... (From what I have read, it depends greatly on how cold you are willing to tolerate the cabin temperature.) As for highway driving, my daily commute is just over 30 miles one way, half of which is 55-60 mph on county highways and the remainder 70+ mph on interstate. I can charge at work, so I am always going each way starting with a full battery and have plenty of electric range left when arriving at work or home. I don't see the range suffer noticeably when running on the interstate at 70 mph with the cruise on. I have engaged the HV mode a couple of times when needing to mix it up in traffic at 75-80 so as to not burn through the battery so fast, but I have also driven up to 80 mph in EV mode with no issues. Bottom line is that it is a fully competent highway car. It won't be mistaken for a sports car, but has ample power in any mode for hills or passing. In sport mode the power is very responsive to the pedal.
IMO it is the best PHEV drive train on the market. Some of the electronic gadgets I am still experimenting with but so far find less impressive: The lane keep assist seems to wander and hunt. The adaptive cruise slows down sharply if a car changes into the lane in front of you, even at a reasonably safe distance and pulling away from you, and then takes too long to recover, which starts stacking up cars behind you who now want to pass because you keep slowing down. The lane departure warning triggers at unexpected times, even with it set on the lowest sensitivity. These are gadgets that I am perfectly happy driving without, so I may just stop using those features. The cruise works fine in the standard, non-adaptive mode, and I usually just drive with my thumb on the cancel button.