How much magnification for long distance shooting is really needed?

[VarmLR]

Must admit with my less than 20/20 eyesight I tend to do must of my hunting to around 200yds at 15 times.  Anything under 100yds is closer to 6 or 8x for the field of view.  For years, atop a 22LR I did my first shooting using a 4x40 WA Bisley De Lux scope and used that out to 100yds.  Better eyesight in those days though!