Heh..., every system and system setup runs different. Some might be well configurated and manage a 8x burn even with a PII-266 MHz and some will fail to burn at same speed even when equiped with a 800 MHz AMD.
Why not try it yourself.
Okay, hooked up my new BenQ 1640 currently flashed with EW164B firmware on oldest box at our home (fileserver) and made a test. See attachment.
$ntel AL440LX mobo (system bus 66 MHz)
PII-266 MHz PCU
256 Mb SDRAM
WD 80 GB 7200 rpm HDD
Windoze 2kPro SP4
Only basic progz loaded
Barely capable to burn at 8x...