Headset/Mouse for CoD4

hi,

i right now have a logitech g3 and a speedlink medusa (an ageold version).

question is if an upgrade is necessary and/or recommended for playing cod4 and other tactical shooters.
i was looking into the logitech g500, but i always liked the small g3. are there any good small gaming mice? is it actually good/bad to have a smaller mouse?
headsetwise id like to have a 5.1 or 7.1, although some people told me a 2.1 with fake surround is sufficient. is that true?

as you can see i dont really have much of a clue, so help me pls :)

regards