one Precomp process will take around 20% of your cpu [2cores i3] so using 3 of precomp will take around 80% at most but speed is 3X & yes no errors during packing or even unpacking but instead of wasting 4~6 hours to unpack a single 70GB Folder you will do it in less than 1.5 hour
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one more thing precomp is very slow on larg files but very fast on small files that's what i saw
so if you have a 7GB File I'd prefere to use antiz instead on precomp & if the file is 2 GB of course precomp will be better than antiz
In General PPX2 with precomp is the best way