考官面对那么多的学生，他们如何在短时间内对学生的口语进行评估，主要是下面几点：
1 - Fluency and Coherence.
(what you sound like overall) To get a good mark here you don't want to pause and think too much. Coherence means, can you actually be understood.
2 - Lexical Resource.
Knowing a lot of words is great but you need to be able to use them in a correct way.
Depending on what mark you are aiming for will depend on how you should do this. Keeping it simple and throwing in a few big words might be better for you than trying to use a lot of big words poorly as that will effect this part as well as possibly your Coherency too.
Of course, if you want to go beyond 6 then you will have to "go for broke".