Just want to share some of the posts from our user group blog regarding Windows 7:

http://msforums.ph/blogs/phiwug/archive/tags/Windows+7/default.aspx

Is anyone seeing issues with the RC for Win 7 or R2 on the OptiPlex 760s in term of performance ? Installing Windows 7 on some of these 760 desktops causes for ridiculously poor performance here. One of the processor cores is at about 100% usage at all times for no reason. Installing Windows Server 2008 on a 760 with 8 GB of ram also has this same issue.

"Is anyone seeing issues with the RC for Win 7 or R2 on the OptiPlex 760s in term of performance ? Installing Windows 7 on some of these 760 desktops causes for ridiculously poor performance here. One of the processor cores is at about 100% usage at all times for no reason. Installing Windows Server 2008 on a 760 with 8 GB of ram also has this same issue. "

NVM, we found it:

On the 760s, entering the BIOS and under performance, disabling C states control fixes the issue with Win7 and server 2008 r2 and dramatically increases performance.

Thank you very much for posting back to this thread. This solved the terrible performance problem I was seeing on a OptiPlex 760 machine.

Thank you! I created this account only to thank you for your information.

I just bought my job's old Dell machine and I cannot understand how a "performance" BIOS setup can turn a fine PC into a crappy piece of hardware. It's a shame for Dell.
And all these past years I was suffering with these desktop at work without a solution...