I'm not familiar with Mister Nuff though I'll throw in my two cents; that are not necessarily valued at 2% of current dollar.
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UPDATE #1:
1,645 miles since the oil change - vehicle is at 140,975.
I added .6 qt to bring the level up to full mark.
I think previously, I needed to add a full quart by the 2K mark ...[Then you would've needed at least a 2nd qt by 4k & another half by 5K ]
Update #2:
909 miles since the oil was topped off to full.
2,554 miles since the oil was installed.
Total oil added so far: 2/3qt.
Oil level as of today:[appears about 1\4qt low]
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Odo: 143,017
Miles on Oil: 3,680
Added another 1/2 qt.
Total oil added is about 1.1 qt.
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Odo: 144,211
Miles on oil: 4,874
Currently, the oil level is 1/2 qt low. I did not add any additional oil.
To date, the amount of oil added is 1.1 qt.
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You've dropped from at least 2.5qt to perhaps 1.75qt give or take. You've saved 3\4qt over 5K which is around a third of the original loss. Plus, that early burned oil would not have experienced any cleaning advantage as latter added oil could. It's possible that with a fresh fill you might see additional savings. You've replenished enough oil to continue if you are so of mind. If you wished to save the rest of your Restore, for another project, you could add Valvoline 10w-30 and carry on.
However, 0.6 at 1645 is 1.8qt at 4,935mi. Current claim is 4874mi at 1.6qt. I changed your 1.6 value to 1.75, leaving a 0.15qt buffer of sorts\err on the conservative side, yet you seem to burn consistently since adding 0.6qt oil at 1645mi. My verdict whilst sipping java & crunching numbers is:
Six of one, half a dozen of the other.
Your the one that dropped the coins on the Restore, so it is your call to stop or carry on. I'm not sure how much you would help your cause by topping off with more Restore and running more miles. At this pace of burn\add you might have discovered the sweet spot of 1645mi\0.6qt 10w-30 Restore. Who's to say?
When & if you return to using 5W-20 is the only way to gauge any perceived savings. Since this treatment was designed to be used at 100K and you started at 139K it may be prudent to continue your experiment at least to 6580mi on the clock.
Top it off, run another 1645-1706mi and see if it needs another 0.6qts.
Or not, whatever ...
One thing is certain. You will never be at this juncture again.