Use the resolver or SMBiosEFI. But as you got Chamelion 2 installed: use the SMBIOS plist. You can write anything you want into it. Also you don't need any patched kext with it, that will be overwriten by software update (One step nearer than the original).
Just the original Apple one will do.

But why a Mac Pro? We don't have Xeon machines. Change it to iMac 8,1 or 9,1.
For info look at geekbench results: (http://browse.geekbench.ca/)
and you can have any hardware fake you want for the plist.
Also see http://www.everymac.com/ for specs on Macs.