Rapha, nice but a bit pricey?

Whats the fit of the merino arm warmers like.

I'm a large in terms of circumferance, and a small in terms of length.

Logically a medium seems the way to go. But will I be better off getting a small so avoid bunching? or a large to avoid over stretching?

My M/L endura armwarmer are too tight to wear.

I use M in the standard arm warmers. I have pretty bulky arms and am 5"6 so not the longest of arms. No real bunching at all and S would be too tight and L would be too long.