Will be nice to see a dyno chart for a full termi exhaust.
I would expect very little or no noticeable difference. The full headers may be slightly smoother lacking the O2 sensors and the exhaust valve but they're not any larger than the "R's". The reasons for swapping are for the farkle ( a pound less weight) and bling (shinny and blue).
For major performance enhancements, I'd first look at fine tuning the AFR, gearing change and lighter wheels followed by larger throttle bodies, higher lift cams, lighter connecting rods, etc.