depends on burner and media. my laptop with ritek g04 only way for good burns is at 1x or 2x speed. main machine with sony dru 500 latest firmware same media i can burn all day at 4x with no problems apart from the very occasional sub standard media. All i can suggest is start of at slowest and work up your speed until back up's dont play well.
i found with my matix infinity chip that i can burn at any speed and not have one skip..... the only skips ive had with that game are from scratches......
swap magic however, the lower the better, of corse some games skipped even at the lowest speed...
matrix infiniy modded ps2 (broken, burnt out PS1 fuse)
xbox(freshly softmodded with krazies)xbmc dash. Stock HDD.
www.norcalmods.com did my ps2 mod, cheap n fast:)
DOWN WITH APPLE!