There are a few great posts on the web on how to speed up your phone. I won’t try to re-create them. I personally like the version from lifehacker and the few links they have related to Battery life and settings
http://lifehacker.com/5897438/how-to-speed-up-clean-up-and-revive-your-iphone
Overall, the idea is to disable anything that is continuously talking or communicating to the web. Basically, notifications and location services.
I have not upgraded to a 4s yet, but a major reason I would make the change is for performance. My 4 is not the fastest thing at the moment. However, it is good enough. I have done a quick race with my wife and her 4s is quite faster.