I've only heard "beer gas", never G-gas, until today.
So anyway, because the beer gas is 75-25 on my setup I can carb at 5 psi and then push at 20 psi with no additional carbing occurring from the co2 in the beer gas. I do use co2 only to force carb.
On Tap: 1. Kelly R. IPA, 2. Roter Hund Hefeweizen, 3. Bud Killer Blonde, 4. Red Dog Pale, 5. Roter Hund Oktoberfest, 6. Pumpkin Ale, 7. McRed's Stout (with new nitro system and stout tap,) Cream Soda, 8. ESB # 3, & 9. Ordinary Bitter.