This test did not go at all, as I expected. But I think we can draw some conclusions here, and close the experiment. Namely, that @Mammoth is correct, in that 4-8 GB of RAM not being enough for Bitcoin is not a general Bitcoin problem, or a UTXO set problem, but a Bitcoin on StartOS problem. Now, I did notice that the default Knots for Ubuntu setup has a setting to not verify previous to a certain block. I don’t know if that’s the case on the other implementations. This might explain one reason Knots on Ubuntu completed faster, but this does not explain why Bitcoin on StartOS comes to an absolute crawl in the last 20 - 30 percent.
I think @morelub is on to something here. Some optimization of Bitcoin on StartOS might be worth consideration. Or at least better understood, and better explained on our part. Simply assuming that the UTXO set vs the RAM, is causing an unreasonable IBD time, does not appear to be correct.
With regards to Bitcoin coming to a crawl, @ThatLinuxDude did an interesting analysis that might be related.