This my first post here so take it for what is worth.
1)check the wire-feed rate. Set each machine at 350ipms run it for 60 seconds-measure, which one is closest to matching meter setting?
2) get a bottle of c-16 to 20. go as low as you can with short circuit settings- which one maintains a stable arc with the lowest voltage setting?
3) using same argon/co2 mix, install an .045 wire, and max the voltage. Start the wfs @ 350 and increase from there. This wire can handle more current than either of these machines will produce. So knowing this increase wfs at some point past 425ipms one of them will fall outve spray arc and the wire will start crashing into the puddle.
4) Short circuiting using 100% CO2 may also prove interesting. Try some short circuit settings- which one has the widest adjustment of volts/wfs, before you get splatter-rama. should not take long for either one since straight co2's arc range is small.

Or you could save yourself the trouble and get the red one.... ha ha , but at least the test will give you something objective to base a decision on.