JB often makes the device more sluggish. It's kind of the major downside to jail breaking... not a selling feature on it dude.
Battery life will dependent on what jailbroken things you install. Remember, jailbroken apps don't need approval from apple or get tested for performance
The JB itself only increases boot up time. If the device is sluggish, an app is to blame or you're doing something wrong. The same is true for battery life, it's an app or user error.