Cost vs return - aka worthiness debate

[elit]

So, I have made my own repacks "couple" of times before. And one thing I repeatedly kept stumbling upon was how certain(often propagated) extreme compression methods were just not worth it. And I always wondered if I missed something or what, because in all my cases extreme compression methods that took like half day gained at most 1% or less than those that could finish job in 1-2h.

For example, packing Project CARS 2 with (freearc)srep:m5f+lzma:mx took I think ~5h and rendered about ~25.4gb from +-40gb. With srep:m3f+lzma:m5 it took about 1+1/2h and I got 25.68gb. And a lot of that time was probably disk bottleneck. There is a huge speed difference on FreeArc between -mx and -m5 as -m5 utilize all 4 cores and other speedups. I understand LZMA is more effective with 1-2 cores instead of breaking data to blocks, but I just dont see much benefits of it - at least if used with srep.

Another example like above was Ghost Recon Wildlands, with similar ridiculous ratio. In fact every single time I decided to "ok lets try on this one again", -mx option simply wasnt worth it. I saw bigger difference only if I did not used srep, then sometimes it really helped more(but not groundbreaking more either), but with anything chained from srep it just didnt do much better. In fact for one or 2 cases(I dont remember which games anymore), srep did the job and lzma gained 0%, you could pretty much just srep them and be done with it.

And if that wasnt enough, I tried to replace default FA's lzma, I tried srep+7z, then srep+(horribly-slow-at-max-settings)xz, and it wasnt worth it at all. Like, say 1.58gb with max xz vs 1.61gb with FA -m5. Thats nothing and one took at least hour+ to do it while other only around ~5min.
Oh and sometimes, FA's -mx gave me few kb bigger archive than -m5!
Hell I even tried zpaq -m4, that one gave better ratio when alone only(vs lzma without srep) but not better when with srep+zpaq or vs srep+lzma.

But I keep reading everywhere people like to chain srep with xz or 7z or whatever and I wonder... why?
With srep at least, even -m5f if fine and quick enough, but this extreme lzma BSDM fetish puzzle me.

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So with that said I would like to know, if you have different experience and you tried that FA's -m5 to compare, can you tell me where you got that significant difference, at which game and how much better and with what parameters? What game can you confirm to see better ratio worth bragging about with srep+lzma:mx(xz,7z) vs srep+lzma:m5? Remember only with srep combined.

Thanks for discussion .