Thanks for the advice Guy,
So I recorded a few clips both on the camera and on the R-05 using all combinations of R-05 built-in mic, Nikon ME-1 mic, Roland CS-15 mic, on both camera audio, R-05 audio and compared them.
First thing I noticed is that the R-05 records in 32-bit and the Nikon D600 16-bit.
Looking at the waveform in Audacity there was no doubt that the built-in mic on the R-05 recorded a much wider range and I could easily hear it in playback.
The ME-1 sounded next best and had the middle range waveform. The CS-15 has the lowest waveform and has audibly duller sound - although in close it improves dramatically. So I think I'm going to stick with the ME-1 on the camera and record to the R-05 with the built in mic, keep the CS-15 for interview/close-in and see how that goes for a bit.