whats happens to most people, over time, is that all the porn they watch and random or accidental visits to bogus websites, bit torrent downloads, your friends "downloading something cool they want to show you", and so forth, starts adding up spyware, malware, shitware and fuckware on to your computer
and in MY experience, no amount of anitvirus, firewalls or any other bullshit can prevent that crap from piling up, feeding on your precious resources and bandwith.
so keeripes has it right, if you truly want to maximize your rig, reformat everything, including any spare harddrives.
reinstall a fresh OS, download all the updates, turnoff as much windows junk as you can, and then install ONLY GAMES
do not install messenger, torrents, movies, or anything other than games that requires or would like a connection to the internet, (including porn)
if you only have 1 gaming machine you can either go the dual boot option, altho i am not familiar with that at all and honestly would not recommend installing two instances of windows on the same machines unless you have two completely separate hard drives.
or just do a total system reformat atleast once a year (or more often), the only downside of this is about 4-5 hours wasting installing everything from scratch, but believe you me speeds go up (not just gaming, overall system performance)
i also recomend replacing your harddrive alltogether once every 2 years, the harddrive is the one part of your computer that wears out due to mechanical operation and burning.
and finaly, some bragging on my part
back when i installed fresh and played on this new TD server, i was getting between 3-5ms connection VIA net_graph 3
to this day, when a new map loads, unless i got a lag spike, i am ALWAYS the first person to join the server ^_^
suckers.