Running the XPDM driver on WES7 is definitely a "legal" option, however, if you have an application (like remote desktop) it may require a WDDM driver to operate which might exaplin the RDP blue screen- poor testing by MS for legal display driver options.
To change GMA, you need to make changes to the VBIOS image in the BIOS image on the board. That uses a utility called 'BMP" to change options like spread spectrum operation that generally is only available to OEMs (I do not know your customer status). Additionally this capability usually requires close work with your BIOS vendor to get the appropirate merge tools for their product.
As you have found, the IEGD driver allows you to make these sorts of tweaks much easier, but primarily for a more embedded envirionment that the GMA drivers do not want to provide as it tends to mess up WHQL compliance, and is dangerous to put into end-user laptop / desktop users hands.
To adjust spread spectrum, you may be better off figuring out how to use the IEMGD driver...
Hope this helps.