Here is how divider really works.
When your CPU is running at 289x9=2601, and your memory is set to 5:6, the memory speed is calculated in the following way:
9*6/5=10.8; the CPU rounds this number to 11, so your memory is at
2601/11 which is about 236. It is NOT 289*5/6=240, but some programs and/or BIOS will report this number.
Here is a list of dividers used for a combination of CPU multiplier and memory divider setting, it's in the form of 183 - x8->x9, which means when you set your memory to 183Mhz in the bios and the CPU multi is 8, the memory is running at 1/9 of CPU speed.
mem divider:
200 - x8->x8, x8.5->x9, x9->x9, x9.5->x10, x10->x10, x10.5->x11, x11->x11
183 - x8->x9, x8.5->x10, x9->x10, x9.5->x11, x10->x11, x10.5->x12, x11->x12
166 - x8->x10, x8.5->x11, x9->x11, x9.5->x12, x10->x12, x10.5->x13, x11->x14
150 - x8->x11, x8.5->x12, x9->x12, x9.5->x13, x10->x14, x10.5->x14, x11->x15
143 - x8->x12, x8.5->12, x9->x13, x9.5->x14, x10->x14, x10.5->x15, x11->x16
133 - x8->x12, x8.5->x13, x9->x14, x9.5->x15, x10->x15, x10.5->x16, x11->x17
125 - x8->x13, x8.5->x14, x9->x15, x9.5->x16, x10->x16, x10.5->x17, x11->x18
100 - x8->x16, x8.5->x17, x9->x18, x9.5->x19, x10->x20, x10.5->x21, x11->x22