(This was a comment of mine on another site, but I decided to post it here for discussion.)
Note: These are relative comparisons and they are exaggerated for comparative clarity.
Sx/Sp's believe in freedom. And they don't just believe in it as an abstract concept, but in reality. They don't want to be held down, confined, restricted, or contained. But then there's the problem of their siren, their drug, their love...an Sx/Sp would sell their soul to merge with their object of desire (be it a person, idea, or whatever). They will tirelessly fight off all other chains placed on them, but they will willingly don the handcuffs binding them to their love. The Sx/Sp ideal is to run away with their love and leave all the world behind.
Sx/So's will not do this. Freedom is too precious to surrender, even to the object of their deepest affection. The Sx/So ideal is not to run away but to stand and fight, tearing down the walls and breaking all chains. Their siren, their drug, their love...this is the greatest chain of them all. They have a strong desire to merge and yet are compelled to at least put up a token resistance.
2. Means to an End
The Sx/Sp places their hopes for fulfillment of their primary instinct (and ultimately, their survival) in their personal qualities and attributes: attractiveness, charisma, skills, abilities, success, wealth, status, etc. When things don't work out, this can leave an Sx/Sp feeling self-conscious. This gives Sx/Sp's an aire of self absorption and, in some cases, fatalism.
The Sx/So places these hopes in their cunning, cleverness, and ability to make the right choices and decisions. When things don't work out, an Sx/So may wonder what they could have done differently to have more success. This makes Sx/So's come off as enterprising masters of their own destiny.
Let's take seduction as an example: an Sx/Sp focuses on seeming desirable and attractive, an Sx/So focuses on saying the right things and acting the right way.
3. Romantic Relationships
Both Sexual types exhibit a push-and-pull dynamic. The Sx/Sp's version of this is the classic iteration: intense, passionate desire suddenly becomes too intense and Sx/Sp pulls away to protect themselves, only to have the desire return again.
The Sx/So push-and-pull is an internal one: drawn in with some hesitation, drawn closer, maybe pull back a little, still drawn in. It doesn't look as extreme as the Sx/Sp dynamic because the Sx/So doesn't completely surrender to their desire.
As a result, an Sx/Sp is going to be more all-or-none in relationships, either on out on the sand or drowning in the depths...possibly bouncing back-and-forth between the two with the tides. An Sx/So will be more balanced and stable in their relationships, preferring to wade in the shallows.
Additionally, an Sx/So has a much greater problem with partners that seem clingy or smothering. This is encroaches too greatly on their freedom. An Sx/Sp won't have a problem with this in itself (and may even like it); their greater concern is the desirability of their partner. Extreme closeness with a confident and secure partner is Sx/Sp heaven, with an insecure partner it's hell.