Zooma,

I'd say you're quite right to maintain a constant thickness of underclothing. Personally I think technical fabrics are better than cotton, warmer in the winter, and cooler in the summer. Cotton tends to get damp and claggy in the heat.

I shoot on an uninsulated and unheated range; wool long johns make a big difference in the winter.

There is one advantage for tailored sleeves in 10m air, a pointier left elbow should dig into your side better than a loose sleeve.