EVGA recently released a BIOS update (Revision SZ2Z) that enables HPET support in the system's BIOS.
What does this mean? It's quite simple, it means that people with EVGA's X58 motherboards can now have vanilla speedstep.

WARNING: This guide involves flashing your system's BIOS with a newer revision. ALWAYS Follow the onscreen instructions during the process. DO NOT remove the floppy or CD-ROM until it says it is safe to do so.

First, visit this thread to grab the update, and for flashing instructions.

After you've completed the process, follow these steps to enable speedstep:

First, your BIOS settings will be wiped out during the update. The first things you will want to do is:
1. Go to the Integrated Peripherals menu
1a. Go to Onboard PATA/SATA Devices
1b. Set the SATA Mode to AHCI
1c. (optional) Set the JMB363 mode to AHCI + IDE (this will allow OS X to natively detect one of the two JMicron controllers)

2. Go back to the main menu, and go into Power Management Setup
2a. Enable HPET support
2b. Set HPET Mode to 64-bit

3. Go back to the main menu once again, and this time go into Frequency/Voltage Control
3a. Go into CPU Feature
3b. Enable Intel Speedstep
3c. Set the CxE Function to C1E

After doing this, save your changes and reboot to OS X.

Go into your Extras/Extensions folder and remove Disabler.kext and NullCPUPowerManagement.kext (and any equivalents), and reboot using verbose mode (optional, but always useful for watching for any issues).

After the system has rebooted, you should now be using Apple's native SpeedStep drivers with no issues!