Same here,
It seems the R3 is slower for me than the R3rc2. When I say slow I mean it literally takes 8 hours for encoding a x264 8 min long video (on an i7 7700k) where it tooks around 25 min before.
However this problem only occurs in Premiere Pro and not in Media Encoder, for me when I launch Media Encoder and add a video manually then launch the encode, it is working perfectly.