There are different theories about the possibility of unlikely or clashing enneagram+MBTI combinations. Some claim that some combinations are impossible, Others, like
Pat Wyman, claim that almost any combination is possible, but some combinations clash more and are extremely stressful. In her view, people with dissonant combinations must either work through their unhealthy enneagram defense systems early, or suffer from stress, lower functioning, and other negative side effects.
I would think being extraversion would be hard for a 5w4. The gap between 5 and 4 at the
bottom of the enneagram is sometimes called the "existential gap", and is the most inward-facing area of the enneagram (flanked by identity-via-thought and identity-via-feeling). Hence, it seems like being an extraverted 5w4 would be difficult to sustain, especially with the 5s tendency to withhold and withdraw.
Type 6 can also be very rational and analytic, and seems more neutral as far as introversion/extraversion goes. It might be worth considering the influence of your 6 wing, as well (just as you've done with your security point)... I could see the 7 considering of possibility combined with a 6 need to test producing a lot of analysis. (Not saying anything definitive, just suggesting.)