My fuckbuddy has much the same mindset as subgirrl. No matter how appealing it sounds at the beginning to have long, luxurious, sensual, intimate, slow sex by the time we've been going at it for fifteen minutes or so she gets so horny that she loses control and can't help but whip into a frenzied session of hard, fast fucking.
You should really convince her to abstain from the hard finale at least once. Part of what makes a truly mind blowing orgasm at the end of a slow sex session is that you never fully give in to your carnal desires -- something is left out all the way along as you deny yourself the fast and aggressive end. However, when you finally do get to reach climax through that slow and gradual build, it's just that much sweeter because your not in the "zone" you're both so accustomed to.
The issue with talking about this stuff is it makes me horny