This worked on the iPhone 3G on iOS 4.2.1. Does it make iOS 7.1 faster on your iPhone 4?
Whether it speeds up the device, I cannot say, but I make it a habit of disabling certain things in the search option. For instance,
1. Music
2. Podcasts
3. Videos
4. Audiobooks
5. Voice Memos
6. Messages
I don't stockpile the above so there's no need for me to use the search function for them...