in the little metal box they locked my in for my last job it ranged from 130F to -15F. which is 54C to -26C. as fun as the hallucinations and heat stroke was i much preferred the -15F/-26C
right around freezing was most comfortable to work in
Old School
Perfect weather for me would be like 60F (~15.5C) and overcast. Hottest temp I've ever been in was I believe something like 115F (46C) while at the Grand Canyon. Have only ever been in below-freezing temperatures once.