Have you tried using external GPS connected to the phone through BT as a data source ?What? I think we might not be on the same page.
I do get speed, it's just annoyingly inaccurate because it's derived from slow iphone GPS.
I'll have to check out the link you provided cause the in-app settings don't seem to allow for OBD-derived speed. From that link, sounds like the app defaults to GPS speeds and Race Render defaults to OBD speed. I haven't put my most recent track data into Race Render yet so that might be the easiest fix.