QUOTE(Pheidias @ Dec 13 2006, 07:41 AM)

a dvd9 is 8.5 GB, or in reality 7.92GB and according to most speculations the usable space on a x360 dvd is 7-7.2GB which would mean the security sectors to take up 700-900MB.
Wrong, did you not understand the numbers you posted that you got from wikipedia?
QUOTE
DVD disc capacity
Physical size GB GiB GB GiB
12 cm, single sided 4.7 4.38 8.5 7.92
12 cm, double sided 9.4 8.75 17.1 15.93
8 cm, single sided 1.4 1.30 2.6 2.42
8 cm, double sided 2.8 2.61 5.2 4.84
Note: GB here means gigabyte, equal to 109 (or 1,000,000,000) bytes. Many computers will display gibibyte (GiB), equal to 230 (or 1,073,741,824) bytes.
Example: A disc with 8.5 GB capacity is equivalent to: (8.5 x 1,000,000,000) / 1,073,741,824 ≈ 7.92 GiB.
DVD9 is not " in reality" 7.92GB. It is 8.5GB or 7.92GiB. THERE IS A DIFFERENCE. Read the bold text if you do not understand.
SO 1.5GB of reserved space for 'security' it still a ridiculous amount.