You really have a choice when you import 601/709 or RGB. You can see the difference by importing any test file, importing that file both ways, then drop each on the timeline, and looking at the waveform monitor. An XDCAM file imported(or transcoded) to 601/709, will be imported so that any luma values outside of the video range of RGB16-RGB235 will appear as white on the WFM, indicating they will be clipped if you export to 601/709. On the other hand, if you import with the RGB setting, all out of range values will be remapped to within the RGB16-RGB235 range, and, again, you can see this by importing the same clip both ways, and looking at the WFM display for each.

A couple of side observations:

1-Not all HD cameras are the same. The Sony EX1 records values in the superwhite range, i.e. RGB235-RGB255, if you shoot in all modes except CINE2. CINE2 will force the EX1 to capture all luma values in the legal range of RGB16-RGB235.  If you shoot any other setting, import as 601/709, you'll see the superwhites as white on the WFM

2-You can import an XDCAM file with 601/709 and apply a gamma curve(via the CC plugin) to bring the out of range values back in range. If you apply the CC correctly, it will be identical to letting Avid do it with an RGB import option.

I hope this makes some sense to you. If not, make yourself a SMPTE color bar test clip and import the test clip both ways. Then study the difference with the MC waveform monitor.

Many thanks for those who contributed to this thread. I will sure do some tests as suggested and see what works best.