As I said above, visually no, it wont do anything more noticable (I did the exact upgrade your contemplating now). It will lower cpu usage slightly but increasing loading speeds of menus and such I doubt. If you have another motive for upgrading (like connectivity like I did) then youll find it worth it. If its just for the DX9 certification, I personally dont see it worth it.
Just to compare basically, you said your current system tv load is about 30%. With my setup as stated below, I see usually jumping between 17-30%. So not a huge amount of difference.