That's a tough one. Despite all its known issues, G04 was nevertheless, indeed, a fantastic disc for compatibility with players and consoles.
You could try 16X -R Verbatims (MCC 03RG20). I prefer the 8X version for my personal use, I get better testing results with them, but the 16X version seems to have a better reputation for great readability among players.
I think I remember someone with a gamecube saying he had good luck with bitsetted CMC MAG E01 (8X +R), but with these your burner will be an important part of the equation (it must be able to bitset the disc to ROM and burn it very well!). Also you need to find premium grade CMC MAG E01: the HP-branded ones are excellent but most E-net stuff with this mediacode (Datawrite, Datasafe, Ridisc) is mostly mediocre.