I found a partial answer to the question I was curious about – does it matter whether you just spent 15 minutes with a sick person or whether you were sitting in the same unventilated room for hours? The paper below gives a clue:
among admitted to the hospital in 2020, chances of death was 5x higher for those with high viral load at admission v. those with low – about same as difference between 30 y.o and 65 y.o.
Of course, viral load may be a factor of how disease is progressing. They have another clue – how viral load changed during first weeks of pandemic in 2020, when people became aware and started practicing SD. Low viral load went from 30% of cases to 70% in one month. So, seems like level of exposure is important.
SARS-CoV-2 infection: Initial viral load (iVL) predicts severity of illness/outcome, and declining trend of iVL in hospitalized patients corresponds with slowing of the pandemic
Said El Zein, Sep 2021 PLOS