Welding with CO2

I asked a welding instructor I used to teach with what to expect using CO2 instead of 75/25 and he said the following:
It will be fine. Usually takes a little more voltage. But often runs a little hotter than the mixed gas. A -6 wire would be better than a -2 wire. The -6 has additional anti-oxidizing additives and the -2 is for flat or horizontal welds. He also said it may have more spatter to use just co2 and that is why the mix is preferred for sheetmetal.
Hope that helps. I didn't ask about the regulator...that may have been an unfortunate coincidence I'm thinking.