If you're shooting a 4x in the field, how much precision do you need above and beyond what you are capable of discerning with the 4x? If a 20x scope helps tell the difference between a .75MOA load and a 1.25MOA load, is that really going to matter on a game animal when using the 4x as the "aiming device"? I know it's mentally helpful to have faith in accuracy of a load, but I'm not sure I'd fret it too much if it shoots acceptably for me at hunting ranges with my intended optic.
That is more or less my view too.
FWIW you can make things easier for yourself by attention to the aiming mark, to make it suit whatever sight you are using. With a scope which has a crosshair reticle IMHO the best aiming mark is an X, preferably one where each of the four "legs" of the X are tapered - thick at the extremities and tapered to a point at the centre. It is easy to find the centre with such an aiming mark and it compensates for the lower resolution. Much better than the various squares and diamonds and so forth.
With the right aiming mark and an accurate hunting rifle I can be quite confident of shooting groups well under 1 moa with a 4x scope, and for the sort of rifle on which I have a 4x scope that is plenty good enough.
