Interesting from a Windows Insider Program email just now -- although I'm no longer using the Insider Preview builds:
<< If you want early access to key updates - but also want less risk to your device than being on the Fast or Slow rings – the new Release Preview ring is your best option.
Just go to Windows Update>Advanced options>Get Insider Preview builds and select Release Preview. >> [My emphasis here]
Note the RELEASE word in what you select -- Must be getting really close.
I must look and see if that's available on my RTM version of 10 and/or on 8.1 ... and maybe sacrifice one of them!