...and first and foremost listen to your own instincts. Women may have high tolerance for pain and may also get off on daring you and themselves to go farther and farther but if you feel that putting more muscle into it could cause real damage you still may want to restrain yourself. There were cases when women challenged men to get rougher with them and inadvertently ended up meeting their maker.
Be especially careful if her idea of getting rougher involves strangulation. Suffocation is only one way things could go wrong there. Neck is notoriously fragile part of one's body and could be easily broken. Both of you may not even realize that you're approaching the breakage point, especially if you're physically pretty strong. Google it, you'll see there's been plenty of cases of such things happening.
No matter how far you take it it's bound to get old and mundane after a while, so you'd be tempted to take it a step farther. Some people like to challenge themselves into taking it to the limit.
There's a movie I'd like to recommend. It's a old Spanish movie from the 80s, called Matador with young Antonio Banderas. Your GF I'm sure would also love it. Sure it describes a really extreme case but make no mistake things like that are out there, and it usually starts with getting rougher and rougher, challenging the borders, walking the edge, approaching the borderline.
My personal suggestion is if you feel yourself approaching unreasonable limits, you may want to diversify your experiences. Both atmosphere and situation-wise and, depending on how open-minded and confident in each other you are, maybe even partner-wise. Many women love to go at it with other men with their SO either participating or watching. I suspect if a woman likes it rough she may also appreciate that too. ...or may not. Most of the men don't like such things happening but I suspect most men don't take it to your level in regards to rough sex too.
Just saying