You are conflating mouse lag with intentional mouse smoothing. What you are experiencing is a performance issue rather than an intentional manipulation of mouse response. Try some of the performance tweaks listed elsewhere on the forum- specifically the d3d9.dll fix for your brand of graphics gpu.
yeah thats definately not mouse smoothing.
make sure your not running vsync since that always induces a delay.
everything else i agree with charybdisjim
tweaks guides is also helpful as well.
not all mouse related will be fixed until they ever decide to upgrade the software mouse rendering into hardware based. but i doubt thats gonna happen sicne they will moving to a better engine for the next installment in the series. and from i can tell, the engine they will be using wont have any mouse related issues due to the options available. unfortunately its a waiting game until the next game and isnt a solution.