If 80% or greater Argon mix is used and up to 90% both metal transfers (short circuit & spray) can be made. One gas - both transfers and if gage sheet metal is the predominant product; use the lower argon, if thicker metal is predominant; use the higher argon. Or, try out the various mixes and see which will have the greater operator appeal. Using a gas with more argon than the 75/25 will change the arc sound. If welders are setting short circuit metal transfer parameters based on the "Bacon Frying" sound, gas changes will make a sound/audible change. If the welder ain't happy, ain't nobody happy! Set the parameters with volts & amps and fine tune the arc with the inductance control.
Different gas distributors package different mixes such as: 80/20, 82/18, 83/17, 85/15, 87/13, 88/12 and 90/10 as standard offerings. The higher CO2 content will provide greater penetration in the short circuit transfer. The higher argon content will make it easier to achieve the spray transfer. How many gas distributors are vying for your business? They may lend you a cylinder for testing. Or, use a Smith Gas Mixer and mix your own.
Write the procedure with a specific gas percentage mix. Don't use the gas distributor's fancy dancy labels like Moon Gas 1 or Star Gas 3.