You want the best compatibility for the drive, and the drive is quite picky. Burning slow makes darker pits, which are easier for the picky drive to pick up on. I've burned games fast and slow on the same media, and I found that burning at 4x is the sweet spot for me. 6x always ends up making coasters (failed burns), and 8x, 12x, and 16x fail to boot in the PS2. (Using Swap Magic 3.6 boot disc to enable backups to play)