Slow burning speeds on toast and disco

[cnone]

i have amd leo4all v4.1 leopard 10.5.4 installation with voodoo 9.5 kernel.
my cpu: amd athlon 6000+ on asus m3a with sb600 chipset

my performance issue is: i can't burn my dvd's at supported speeds like 12x or 8x, sysprofiler says media supported with 12x burning speeds, recognizes my drive as generic burning support but everytime i try to burn my dvds at that speed toast writes it at 1x and then tried disco.app too, still no luck at higher speeds. am i missing something?
my installation works perfectly and qe enabled by the way.

is there anything i must do to force the dvd writer to burn higher speeds?
is there any system settings i check or drivers i must install?

ps: i don't know is it relevant with this but my installation boots slow too, it takes approximately 2-3 mins

thanks in advance..