Professional Second Banana
Sounds like you've basically got the same PC I do - like I said above, my computer becomes seemingly frozen for about 5 minutes when the NMF operation starts. After that, I regain control, but my RAM is completely maxed out until 2 or 3 of the 8 NMF tasks complete. If you're encoding longer videos like I am, I wouldn't recommend using your primary PC for NMF since you won't be able to run any other apps on your PC for quite a while (a ~5 hour run capture takes about 18-20 hours to NMF and encode for me, so I use my laptop that has 8GB and a similar processor for HQ encodes).