Kirk Lowery wrote: ↑January 10th, 2019, 6:48 pmis this normal syntax in Koine?
Yes.
Kirk Lowery wrote: ↑January 10th, 2019, 6:48 pmis this Luke showing off his education?
Yes.
Kirk Lowery wrote: ↑January 10th, 2019, 6:48 pmIf this is not normal usage, then what is being highlighted by the author?
I take these sort of structures as syntactic evidence of the Greek's prosodic structure. There's literature on this, but there is no satisfactorily unified account just yet...even though it all points in this direction--the debates are in the details.
The tendency is to place the sentence accent at the front of the sentence. In turn, then, when the speak/writer wants to place the sentence accent on something other than the default position (the verb), he will move it forward. Normally the pattern is to split an NP constituent, whether in a PP or not.
But Stirling's example from Clement is much more fascinating since its only the preposition ἔξω that is fronted. That particular pattern is far less common in the Koine.