community user report "the 2.6.4 BIOS will allow the CPU update to Q6700, and it is required"  your current bios 2.6.4 (circa 2010) is good for Q6600.
Hello. I got hold a of 745 MT and I have successfully updated to BIOS 2.6.4. However, when I try to install 2.6.6 version I get the following message:  [IMAGE] I have run it as Administrator both under win 7 &10, tried to launch it via bootable MSDOS usb key but everything ends up the same way.  Reason is I want to install a Q6600 inside will I be able to use it with BIOS 2.6.4? Current config is C2D E6400/ 6 GB ram Thank you in advance. 
Optiplex 745 MT BIOS 2.6.6 update payload error