Speed is crucial in most of the sport, the fastest car, fastest goal, fastest lap, fastest boat and so on. And speed is one of the thing that motivate people to improve. But in sex, it's one of those thing that you don't want it to be fast, the slower the better, of course it depends on the situation as well. Both of you are short of time, and you need a quickie, then it's better to make it fast. But if you have one whole day, you do not have much to do then why not make sex more interesting and spend some time to make it slow?
Girls do like to make it slow, guys always rush in sex, they want to penetrate whenever they are erect. And in most cases, girls do takes time to get wet and ready for sex. If you think 30 minutes is good, double it and make it an hour for sex. I do not mean one hour is good, but it does enough for most of the girls. If you spend more time on stimulation, the bigger chance that they have an orgasm, and the bigger orgasm they have.
Slow is good for guys as well. Are you sure? Ask yourself how long you can be ready to sex again after ejaculate? It will take you some time to erect again, so why not take it slow and steady, give her a big orgasm to satisfy her. If you ejaculate to fast, it may not be premature ejaculate but your sex partner may not even close to orgasm, you do not want that to happen. Take it slowly, it will do you good. One thing does apply to men as well, the longer you hold the bigger orgasm you have, right?