Sure, but what about when you eat? What about when you're exercising? My point is that caring much about filtration efficiency quickly stops mattering after y

Sure, but what about when you eat? What about when you're exercising? My point is that caring much about filtration efficiency quickly stops mattering after you've done the obvious things, because there are simply going to be times where you're not breathing filtered air, and those will very quickly become your main source of exposure. This also means that if you feel like you need to get a mask, you should probably get the most comfortable, least restrictive one, even with a worse rating because (say) 90% filtration all the time is better than 99% filtration 80% of the time (if the discomfort causes you to take it off 20% of the time)