I have a retail install with these kexts:

• AppleUpstreamUserClientDisabler.kext
• AppleVIAATA.kext
• fakesmc.kext
• IOAHCIBlockStorageInjector.kext

All in the Extra folder

No NullCPUPowerManagement.kext or OpenHaltRestart.kext or SleepEnabler.kext

so what I would do is:
- copy those to a safe place
- proceed with the rc5 installer
- copy/replace those kexts with the ones just added by installer
- rebuild caches/mkexts
- replace DSDT if any
- see if Themes were added or do it manually from svn
- reboot
- if it booted ok, only then proceed to replacing "boot" file with the one from here

Ok, I renamed the Extra folder, installed the RC5 which created a new Extra folder. Copied my 4 kext to the new Extra folder, copied the Themes from the RC5 DMG file. Started Kext Utility.
I do not have DSDT. Reboot and the result is the same ACPI KP.

anybody else did try the pre-release ?
I 'd really appreciate your feedback before committing. Thanks

@diskeeper,
You need to get rc5 on your own :( sorry! but I don't know what kexts you would need. Do some research/tests. And let me know when ready ;)

Tried the custom rc5 installer, boots just fine.
copied the boot, same issue as before I'm afraid:)

did u tried booting with ForceFSB (in boot.plist) ? which value did u give it ?
what about 5.1.2 ?

hum since my processor and mobo doesn't specify a fsb(uses hypertransport instead) value i just blindly tried 266 but didn't help at all
Also tried 215, which is what my bdmsg has reported in the past but didn't work.

are there any other flags than
<key>ForceFSB</key>
<string>215</string>

I should add to get this working?

nope; but what about 5.1.2 ?

5.1.2 boots, major sound issues though

gimme a bdmesg, plz