I think not that there is an wall...
i drive on fsb 500 on air with my P5Q-E
333mhz strap
5-5-5-18 timings on ram with setting to moderate rest auto
vcore 1,4v ( core 2 duo e8200 )
CPU GTL @ 680
NB GTL @ 600
PLL 1,56v
VTT 1,3v ( because wolfdale dont like high VTT )
CPU margin on optimized
i hope i dont forget something
PS: meine ICQ nummer ist 162569487
Good Luck