People who are not Christians usually do more than just think and talk about it. People who are Christians need to learn how to control it. We are not to engage in lustful thoughts. When an impure thought comes we need to know how to rebuke it and think on Godly things (bring every thought into subjection to Jesus). It's not my rule. That is what we are told to do in scripture.
The best thing to do is pray about it before getting married. Sex is not everything and if a person is compatible with someone and in love and MAINLY if it is the Lord's will then they will be compatible sexually.
Nobody should or needs to make some kind of sexual pact before getting married. Sex is something that a husband and wife need to work out when married. Sex is something that really takes effort, practice, work, and understanding in a relationship/marriage.
Not trying to be vulgar or anything, but haven't you heard the saying you have to do it at least a hundred times with someone before you even know if it is good or not...
The actual meaning behind that is that you have to get comfortable with the other person and work out the kinks together.
Not many people align perfectly during sex, to begin with, it takes time and effort.
Discussing it before marriage isn't going to fix that. It really is something that you have to experience to find out.
And really, would anyone say...I like everything about you, feel like it is the Lord's will for us to marry, but you don't talk about sex so I think I'm going to toss you out.
Like I said before, the main thing is to take it before the Lord and ask His will be done. If it is his will then everything will fall into place...yes, even sex.
If you have nothing on your mind but sex before being married, then you are not listening for the Lord and waiting upon his will. You are taking it into your own hands. And if you end up going against the will of the Lord, then no matter how good the sex is the marriage is doomed.