If I don't set up an smbios.plist, my Snow Leopard installation defaults to iMac8,1 (Chameleon 2.0 default I guess).
I usually use iMac9,1, and for a good reason.
These two Geekbench results were obtained on the exact same installation and hardware configuration - the one with the ~30% higher score is from when I'm using iMac9,1 as model identifier.
 Geekbench.png ( 147.85K ) Number of downloads: 162

When using an iMac8,1 smbios.plist, VLC media player uses up to 100% CPU time playing high definition H.264 video - when using iMac9,1 it doesn't pass 68%, playing back the same clip - the difference is on par with the Geekbench result.
Running VoodooMonitor when using iMac8,1 it looks like my CPU is locked at its lowest P-State, which is just below 2GHz.

Of course this should only make such a huge difference on a system with AppleIntelCPUPowerManagement loaded.
For more information see this post by 18seven:
http://www.projectosx.com/forum/index.php?...post&p=2062

This post has been edited by Gringo Vermelho: Jun 14 2010, 01:08 PM

Yes its very important. Using the wrong model may also load other model specific kext that will give you issues like random kp's (I have seen this with graphics pm). A better method may be to specifically taylor (legacy method) what kext load for your system.

Thanks for the tip man

Yes, for example when using iMac9,1, the system loads the graphics powermanagement profile for the Nvidia IGP in the iMac.

Luckily it doesn't seem to cause any trouble or performance issues but I thought it would be better to have it load a more appropriate profile. So (as you're saying) I use Master Chief's LegacyAGPM.kext which I've edited so that it uses the thresholds and control method/id 18 (0x12) from the MacPro4,1.
 Screen_shot_2010_03_08_at_3.18.19_PM.png ( 119.31K ) Number of downloads: 217

I've attached it here if anyone wants to have a look.
It loads from /Extra/Extensions, don't forget to set your video cards device ID in the plist before using it.

/revised, attachment updated 10.03.2010.
 LegacyAGPM.kext.zip ( 2.5K ) Number of downloads: 129


This post has been edited by Gringo Vermelho: Mar 10 2010, 07:37 PM