Well, never had expirience with Gamecube, so everithing i will tell is just from my general expirience with burning...
DVD-RW or DVD+RW , or generaly any rewritible DVD or CD are bad for any laser , be that console , DVD player or even PC burner you use to burn .
I tried to burn games on them, ones on PS1 didnt work , ones on PS2 did work , for a short time,( i managed to play game for 3 days) but it damaged both my PS2 laser and rewritible DVD as well, so next atempts to burn game and play ended in failure.
So , i limit my self to only burn movies on DVD-/+RW and play them on DVD player, but even that had its price , my DVD player had more and more trouble playing thise discs (as well as regular DVD-/+R) , those DVD-/+RW also stoped working and even my burner on PC was become nerly dead, (it cannot burn Any DVD anymore but can still burn CD) , all that because i repedly burned some 100 movies on some 4 diferent DVD-/+RW discs .
Now, that same burner burned 1000 PS1 games, and some 50 PS2 games, so that may show you how bad is to use DVD-/+RW.
My recomendation, dont use RW, even if they will work on your console.
DVD-/+R are dirty cheap anyway, dont ruin your laser becaise of 0.5-1$ per disc(dont know price for those discs you ask tough).
its mini 8cm dvd blanks