How much would you say the battery went down by? ie how much faster.
Performance and battery are not really affected in my opinion. For one, you can install tweaks from Cydia to actually improve battery life. Take
You must login or register to view this content. for example. It allows you to configure the screen to dim after x seconds of inactivity. So if you put the iPhone down for a bit the battery will not drain at the amount it would at full brightness.
The only thing that will really affect battery performance is installing custom themes from Winterboard. Unless you want themes, don't worry about that for now.
In conclusion, wait for the untethered iOS 5.1 jailbreak is released. It is close but there is no official ETA. Jailbreaking really makes the iPhone better. There is a wealth of tweaks, apps and other modifications you can do through Cydia.
If you ever want help, PM me. I will be happy to provide instructions on jailbreaking or tweaks