I know windows XP and vista limit the amount of connections you can have to peers. Which in theory would probably make your downloading slower. A friend told me that there are ways around this and the solution can easily be found by a google search. I am not sure how fast it will speed up downloads as I have not tried it.
Also enabling Encryption might speed up the downloads as well. But I am unsure I remember reading on Something Awful that cable companies (rogers, cogeco, comcast) have found ways around it. Again only theorizing.