Just for info, I had this problem, i got around it by getting a better GFX card. However the reason for post is that upon researching more intot he issue.
It turns out DX10 had terrible multi threading potential. Its needed for any modern game to play well. DX11 however has good multi threading abilities.
It would be impossible for them to release a patch (from any kind of business sense) to go back and redo multi threading using a DX 10 framework. Its just not possible without loads of work and testing. Like extreme amounts. Its too fundamental to the core game system.
I just thought i'd mention it incase the information offers any peace of mind.
