Yes my mountain bike has flat bars. Are you saying that all flat bars give this aching thumb joint pain (i.e. flat bar hybrid bikes too)? Do drop-down bars not give this pain? Is there another type of pain that drop-down bars give?
I'm now starting to understand what I need. Drop-down bars to reduce drag when it's windy (and it's gets windy here in the flatlands), carbon folks to reduce hand pain, and a bike that can take panniers as a rucksack is causing me a sweaty back. Also a bike with good handling and stability and a more relaxed upright as being a big guy crouching down may not be so comfortable. It's starting to fit together now.
Thanks.