If I'd have worn leggings and long sleeves, ( from my own personal experience, so don't take this as instructional
) I would have sweated my bollox off and got dehydrated.
I find a fair ammount of windchill supresses the release of sweat, so fluids are retained in the system. Blood is pumped to the subcutaneous layer to keep my epidermis warm, which while being a 'waste' of energy, is one of the quickest ways to burn fat. - My secondary objective for riding 100s.
The primary objective being the Brevet 2000 patch.
PS No 'goosebumps' on forearms, so OK.