> Almost all decent filter setups will hit the same particulate equilibrium asymptote with the only real difference being the duration it takes to get there
I'm not doubting this, but do you have any evidence? According to the specs, by definition a MERV 14 should leave at most 25% of all particles size 0.3 microns or larger in one pass, while a HEPA filter can leave at most 0.03%. It's plausible but not totally obvious to me to me that this means that a MERV 14 will leave at most a fraction 0.25^k after k passes (though it's plausible). If so, that would suggest you need around 6 passes through a MERV filter to get equivalent filtration to 1 pass through a HEPA filter. (Airflow might be 6 times as high.)
I'm not doubting this, but do you have any evidence? According to the specs, by definition a MERV 14 should leave at most 25% of all particles size 0.3 microns or larger in one pass, while a HEPA filter can leave at most 0.03%. It's plausible but not totally obvious to me to me that this means that a MERV 14 will leave at most a fraction 0.25^k after k passes (though it's plausible). If so, that would suggest you need around 6 passes through a MERV filter to get equivalent filtration to 1 pass through a HEPA filter. (Airflow might be 6 times as high.)