Spitroasting can be done on any sized woman. Just search it on any porn site.
It's actually a reference to the position of two guys being serviced by one girl, with each guy taking one end of her (one guy at the head and one guy at the rear).
The position resembles a pig on a spitroast. The size of the woman is irrelevant.
Also, pretty sure porking is just another euphemism for sex. People do use it with different connotations, but for the most part, whether feelings are involved or not (usually, the way I have heard the term, feelings are not involved), porking mostly has to do with very energetic and frenzied sex.
Hold on you pleb that is just a normal towerbridge
"I think people should define the word crap" - Kirby007
Join the Prediction League http://www.vgchartz.com/predictions
Instead of seeking to convince others, we can be open to changing our own minds, and seek out information that contradicts our own steadfast point of view. Maybe it’ll turn out that those who disagree with you actually have a solid grasp of the facts. There’s a slight possibility that, after all, you’re the one who’s wrong.