I take it that your mobo is a GA-8IHXP. You should indeed be able to hit higher speeds than 2500 with that CPU. Seems like you have quite many devices in your computer, what Power supply are you using? How many watts?
You can find your motherboard here:
http://tw.giga-byte.com/products/8ihxp.htm
where it states:
CPU FSB / Multiplier / Vcore Voltage adjustable via BIOS
AGP Voltage / Clock adjustable via BIOS
DIMM Voltage / Clock adjustable via BIOS
So you have good control over these things in your BIOS, and I suggest you go to your BIOS and bump up the FSB, and perhaps up the voltages (Don't give the northwood too much, or it might fry. I wouldn't go above 1.75v)
I like BIOS overclocking better than software overclocking.. give it a shot, and let us know.
Good luck!!