I should point out that MBTI and Socionics, while related, are two very different systems. An INTP in MBTI theory corresponds most closely to an INTj in Socionics and vice-versa. I believe it has to do mostly with different definitions of what "P" and "J" mean. I don't want to bore you with too much theory here, but basically in MBTI "J" means that your strongest judging function (thinking or feeling) is extraverted, while "P" means your strongest perceiving function (intuition or sensing) is extraverted. Compare this to Socionics, where the last letter of your type determines if your dominant function is a judging or percieving one.
For example, in the Myers-Briggs system the functional analysis of an INTP looks like this:
Dominant Function: Introverted Thinking
Auxiliary Function: Extraverted iNtuition
Tertiary Function: Introverted Sensing
Inferior Function: Extraverted Feeling
While for an INTJ it looks like this:
Dominant: Introverted iNtuition
Auxiliary: Extraverted Thinking
Tertiary: Introverted Feeling
Inferior Extraverted Sensing
In contrast, Socionics description of INTp:
Dominant: Introverted Intuition
Auxiliary: Extraverted Thinking
Tertiary: Extraverted Sensing
Inferior: Introverted Feeling
and the Socionics INTj:
Dominant: Introverted Thinking
Auxiliary: Extraverted Intuition
Tertiary: Extraverted Feeling
Inferior: Introverted Sensing
As you can see, the two types are almost exactly flipped depending on which theory you are referring to. While I'm an INTP according Myer-Briggs, I would probably be classified as INTj in Socionics (I haven't taken that particular test, but am judging this by the type descriptions). I think it's important that the distinction be made between the two systems in order to avoid further P/J confusion.
As for one type being more likely to be Aspie than the other, I don't know. I would say that most Aspies are probably either INTP or INTJ though.