Sorry to keep bumping this thread but am hoping this is a valuable contribution
So today I learned that the stepping info for each mac model is located in the IOplatformPluginFamily.kext in the plugin ACPI_SMC_PlatformPlugin.kext. In its Contents/Resources there is a plist for each mac model. I was able to copy the speedstepping info from Mac Mini 5,3 into the Imac 12,2 and then get
11/23/12 9:32:49.000 PM kernel[0]: MSRDumper PStatesReached: 16 27 33 38 40 42
these p-states using an imac SMBIOS
much better than just 16 & 42
for my kext, i also put the stepping into mac pro 3,1 plist since it's a fairly popular choice
finally i version bumped the kext and load it out of E/E, so it should hold through future patches (i left the original untouched in s/l/e)
anyways, i'm going to include my patched kext in case anyone might find it useful to get the stepping of mac mini 5,3 w/ either smbios imac 12,2 or mac pro 3,1