Your processor uses the 12 Multiplier and your memory is rated for 250MHz. You can drop the multi but not raise it. Start off with the 11 multi and the DDR400 memory divider. Disable Cool ?n? Quiet in BIOS. Change the HT Frequency to X 4, this will be good till at least 250MHz. Raise the External Clock to 250. This will give you an overclock of 2750. Somewhere along the line you might need to increase Vcore. It will depend on your processor and how far you go.
"Hyper Transport Technology
HyperTransport technology, which delivers a 2GHz effective system bus, is a high-speed, low latency, point-to-point link designed to increase the communication speed between integrated circuits in computers, servers, embedded systems, and networking and telecommunications equipment up to 48 times faster than some existing technologies."
In BIOS, on the Advanced Chipset Features screen, is "HT Frequency" with options such as Auto, 5X, 4X, 3X...
The HT Frequency controls the speed of HyperTransport bus. The spec is 2GHz, you can exceed it but the speed of this bus has little to do with performance. So the common wisdom is to keep it below 2GHz. You will see many people refer to it as 1GHz, which is due to the math, the x 2 at the end.
External Clock x HT Frequency x 2 = HyperTransport bus speed
Not overclocked:
200MHz External Clock x 5 = 1000MHz x 2 = 2000MHz = 2GHz
Now as soon as you start to overclock the External Clock will be greater than 200MHz, hence HT Frequency 4X up till 250MHz External Clock.
250 x 4 = 1000 x 2 = 2000
Commonly Used Memory Dividers
12 multi
DDR400 = 12
DDR333 = 15
DDR266 = 18
11 multi
DDR400 = 11
DDR333 = 14
DDR266 = 17
10 multi
DDR400 = 10
DDR333 = 12
DDR266 = 15
9 multi
DDR400 = 9
DDR333 = 11
DDR266 = 14
8 multi
DDR400 = 8
DDR333 = 10
DDR266 = 12
DDR200 = 14
CPU Multiplier x External Clock = Processor Core Speed / Memory Divider = Memory Speed
2.2GHz
11 x 200 = 2200 / 11 = 200.00
10 x 220 = 2200 / 10 = 220.00
09 x 245 = 2205 / 09 = 245.00
09 x 245 = 2205 / 11 = 200.45
08 x 275 = 2200 / 08 = 275.00
08 x 275 = 2200 / 10 = 220.00
2.3GHz
11 x 209 = 2299 / 11 = 209.00
10 x 230 = 2300 / 10 = 230.00
10 x 230 = 2300 / 12 = 191.66
09 x 256 = 2304 / 09 = 256.00
09 x 256 = 2304 / 11 = 209.45
08 x 288 = 2304 / 10 = 230.40
08 x 288 = 2304 / 12 = 192.00
2.4GHz
11 x 218 = 2398 / 11 = 218.00
10 x 240 = 2400 / 10 = 240.00
10 x 240 = 2400 / 12 = 200.00
09 x 267 = 2403 / 09 = 267.00
09 x 267 = 2403 / 11 = 218.45
08 x 300 = 2400 / 10 = 240.00
08 x 300 = 2400 / 12 = 200.00
2.5GHz
11 x 227 = 2497 / 11 = 227.00
10 x 250 = 2500 / 10 = 250.00
10 x 250 = 2500 / 12 = 208.33
09 x 278 = 2502 / 09 = 278.00
09 x 278 = 2502 / 11 = 227.45
08 x 313 = 2504 / 10 = 250.40
08 x 313 = 2504 / 12 = 208.66
2.6GHz
11 x 237 = 2607 / 11 = 237.00
11 x 237 = 2607 / 14 = 186.21
10 x 260 = 2600 / 10 = 260.00
10 x 260 = 2600 / 12 = 216.66
09 x 289 = 2601 / 11 = 236.45
09 x 289 = 2601 / 14 = 185.79
08 x 325 = 2600 / 10 = 260.00
08 x 325 = 2600 / 12 = 216.66
2.7GHz
11 x 246 = 2706 / 11 = 246.00
11 x 246 = 2706 / 14 = 193.29
10 x 270 = 2700 / 10 = 270.00
10 x 270 = 2700 / 12 = 225.00
09 x 300 = 2700 / 11 = 245.45
09 x 300 = 2700 / 14 = 192.86
08 x 338 = 2704 / 12 = 225.33
2.8GHz
11 x 255 = 2805 / 11 = 255.00
11 x 255 = 2805 / 14 = 200.36
10 x 280 = 2800 / 12 = 233.33
10 x 280 = 2800 / 15 = 186.66
09 x 311 = 2799 / 11 = 254.45
09 x 311 = 2799 / 14 = 199.93
08 x 350 = 2800 / 12 = 233.33
Info borrowed from Abit forums