Sail area. This factor IMO is a primary in the winter. This 2x polyester jacket I wear over everything greatly increases my 'shadow'.... wind/air resistant surfaces. Then the 2-3 layers on my legs.. the sorel boots.. I guestimate an 8-12% increase in sail area... at least. Then the added 12-14 lbs of clothes weight...

For me it's about the cardio workout.. slower is fine.

Be interesting.. for some math type.. to figure the horsepower it takes.. to move a bike with a certain weight.. under wind with sail area. I suggest in horsepower offhand... another unit of measure.. who knows. Some way to quantify the work done.........