Just pulled the newest fan off the printer. I added more clearance for the DP and some flow ribs:
Here is an XTU GPU test run:
This is really tough to read but I super-imposed the first DP duct and the newest one:
What i take from that jumbled mess is that the newest duct is working better (pay attention to the TDP lines), slightly, but better. I ran the duct with the DP slot last night playing Skyrim and it worked similarly to the one without the DP slot. This may sound weird but i think restricting the flow aperture (adding DP port) is helping because it causes a venturi effect and effectively speeds up the airflow.
What I'll do is make 2 versions available, one with DP and one without.
Also, to answer GreyFox's question, the SP3 internal fan is pulling air in at the top right corner so sucking air out by reversing the fan and placing it on the top right corner would starve the fan and would be much less effective. FWIW I've tried putting the fun up there and forcing more air though the internal fan but it does not work nearly as effectively as where it is now. In fact it will still throttle (extreme throttle where it drops CPU temp to 70C) with the fan on the top right.