Help Needed with Raid-0 – Why is my pc not fast using Raid-0 ?

Please help guy’s and girls!
below are my specs;

Mobo – Asus Crossfire II with nVidia nForce 780a SLI SPP Chipset
CPU – AMD Athlon 7850 Black Edition @ 2.8Ghz
RAM – 8GB Kingston DDR2 @ 800Mhz
GRAPHICS – Asus GeForce 9800GT
HDD – Western Digital 800GB with 64MB Cache x2 in Raid-0 (STRIPE) Config

but my problem is that this raid-0 setup is not as quick as my friends pc, an identical pc like mine but he has 4GB LESS RAM THAN ME !!

im from the intermediate level of pc knowledge, still learning, but skills are limited!

please can someone tell me why my pc is over 30 seconds SLOWER than my friends, yet we have exactly the same hardware and software installed ???