The burning speed depends mostly on the recorder and media you are using. I am using Tayo Yuden (TYG02) media rated for 8x. In my recorder (OPTIARC AD-5170A) it works best if burnt at maximum speed.
Burn it at lower speeds and the disc is written poorly. You have to read the information window on IMGBURN and use that information to judge what is the best speed for you to try.
DVDR is cheap so burn a few until you get the best results and stick to that. It's cheaper do that than burn a whole lot of them and later on figure out they don't work because you burn them all wrong.
SCPH-10000_GH-001 SCPH-15000_GH-003 SCPH-18000_GH-008 SCPH-30001_GH-005 SCPH-30000_GH-016(V4) SCPH-30001_GH-010(V4)
2xSCPH-10190, 2xSCPH-10350, 2xSCPH-10280
"**** j0 hackers!"
-Sjeep (As seen on TOXIC OS ELF...)