I have been testing the new NEO DVD-R PREMIUM disks the last few days. (with a Pioneer DVR-104)
This disk , specially optimized for PS2 & Xbox , really has an unbeatable price/quality.
I have been trying on ALL 3 xbox dvd-roms and it works perfect at x1!
I also tried to burn them at x2 (with cracked pioneer firmware) at it worked without problems on the Philips & Samsung drive , even the crappy Thompson drive did boot the dvd , but somewhat slower and shocks when playing FMV's.

This is really a disk with the quality of a verbatim dvd-r , but for half the price.
You can buy this dvd-r from neotechnologies on xboxmods.co.uk.