What is the biggest/heaviest woman you have been with and did you have difficulty making love to her?
She was over 500 lbs and I don't recall any difficulty. I've had difficulty with women smaller than that, though.
Lots of not just physical but mental stuff factors into the so-called "difficulty" of fat sex besides size: shape, experience, well- or not-well-exercised muscles, flexibility, creativity...though anyone who's ever had a fat girl on top could probably attest that they seem to gain 300 lbs. immediately afterward.