After my previous post I changed som setting:

Extreme Tweaker
Ai Overclock Tuner : Manual
OC From CPU Level Up : AUTO
CPU Ratio Control : Manual
- Ratio CMOS Setting : 7
FSB Frequency : 450
FSB Strap to North Bridge : auto --> 400
PCI-E Frequency: 100
DRAM Frequency: DDR2-900
DRAM Command Rate : 2T
DRAM Timing Control: Manual
CAS# Latency : 5
RAS# to CAS# Delay : 5
RAS# Precharge : 5
RAS# ActivateTime : 15

Read to Write Delay (S/D) : Auto
Write to Read Delay (S) : Auto
Write to Read Delay (D) : Auto
Read to Read Delay (S) : Auto
Read to Read Delay (D) : Auto
Write to Write Delay (S) : Auto
Write to Write Delay (D) : Auto
DRAM Static Read Control: Enabled
Ai Clock Twister : Strong
Transaction Booster : Disabled
Relax Level: 1

CPU Voltage : 1.4000
CPU PLL Voltage : 1.52 --> 1.60
North Bridge Voltage : auto --> 1.55
DRAM Voltage : 2.20

CPU Spread Spectrum : Disabled
PCIE Spread Spectrum : Disabled

Advanced CPU Configuration
CPU Ratio Control : Manual
- Ratio CMOS Setting : 7
C1E Suppport : Disabled
CPU TM Function : Disabled
Vanderpool Technology : Disabled
Execute Disable Bit : Disabled
Max CPUID Value Limit : Disabled

I'm still not able to run an FSB of 450....
Specs:

mobo: Maximus Formula
CPU: 6750
Mem: Crucial Ballistix PC8500
Cooling: TT Big Typhoon

What could be the problem?

Thnx!