You can't patch out a slow processor, but Apple does its best.
iOS 7.1 Jailbreak available for iPhone 4: Will iPhone 4S, iPhone 5
How to Downgrade iPhone 4 from iOS 7 to iOS 6.1.3 (Without SHSH
If You Care About Security, Throw Away Your iPhone 4 Right Now
Apple iOS 7 review
iOS 7.1.2 Update Released [IPSW Download Links]
Testing out an iPhone 4S with iOS 7.1.2!
Jailbreak iOS 7.1 / 7.1.1 / 7.1.2 Untethered Released For ALL
iOS 7.1 on the iPhone 4: As good as it's going to get
Is the iPhone 4 still good in 2021? - Quora