I use Spybot S&D to manage my start up applications. Using one of its advanced mode tools, I review the start up list, compare each programme to the BC startup database, and make a decision about what to kill.
The "price paid" is in CPU usage compare to the time to launch an application. For example, if you are in and out of MS Office all day, it makes sense to save time launching it by allowing it to partially run in the background. If, however, you use it once every other day, then the few seconds it takes to open it to use it is better in the long run than having it waiting for you.
Other things to keep in mind. Unless you are playing on line, disconnect from the internet while playing and close all the connexion programmes.
Also, most games have options to adjust some of the graphics and sounds; lowering these can improve frame rate (sometimes you have to experiment with these until you get a balance between high graphics and good gameplay).
Lastly, something as simple as defragging your computer can also help.
Regards,
John