this part pretty much depends on how much you paly and how fast you are at adapting.
using the same distance with a different aspect ratio will be just as different as using another distance with a similar monitor match
the main point you should remember when matching two aspect ratios is that you will not get an identical match on both axis x and y no matter what you do so the ideal is to simply not do stretched res if you want 4:3 do native 4:3 or blackbars that wont affect your aim and will stay 1.1 matchable with 16:9