I'll ride for 8+ hours a day at temperatures between 7 and 27 degrees. It's almost certain that I will get quite cold and/or quite wet at some point on this trip, so picking the right gear can make a huge difference.
I'll be comfy in the cold with heated grips and jacket liner. An excellent semi-permeable balaclava will protect my neck from the wind. Either motocross boots or my touring Alpinestars will take care of my feet. I'm deciding between Carhartts pants and suspender type winter motorcycle pants. Ditto with the jackets, both options nylon, but one much more adaptable for hot weather.
Hot I can deal with if it's not too humid, riding at 40+ in full gear for days. Extreme heat that is not likely on this trip just tends
to put me to sleep, so more frequent cat naps in the shade are in
Staying dry may be a challenge though. The only reasonably waterproof gear I have are the boots - everything else gets soaked fast in heavy rain. Hands and knees are first to go and it eventually gets behind my neck and in my crotch. I have a decent rain suit that helps, but it's a pain to put on and the water finds its way through it too eventually. At the end of a few hundred kilometers in the rain and cold all you want is a warm shower, but you need to dry all that gear off for the next day too.
So, it looks like I have to concentrate on wet and cold combined.
Maybe I'm just over-thinking it. Whatever I bring, I'm sure I'll be sorry I didn't bring something else :) and I'm sure I'll bring a lot I won't need or use.