For 4.2ghz, in the UEFI bios I set turbos 1-4 to 42, 42, 42, 43 <--one has to be higher or lower (41 also works, but it maxes out at 4.1ghz) and disabled EIST (I had to disable this for Mavericks but left it enabled in ML).
In multibeast I used the overclocked i5/i7 SSDT and the patched AppleIntelCPUPowerManagement, which removes nullcpu. I'm using Mac Pro 3,1 smbios right now for Mavericks, but iMac 12,2 worked for me too, and I had Mac Mini 5,1 working in ML and I think it had more speed steps.
"About this Mac" shows i5 @ 4.2ghz, and HW Monitor shows 1.6ghz at idle and 4.2ghz under load. Geekbench is 12000 with my setup.