Running a higher octane fuel alone will do little to nothing for performance. Higher octane does not mean more power, generally it means less. The reason to run higher octane fuel would be to address engine modifications like higher compression.
Generally a stock engine will run best on pump gas rather than a high octane race fuel. Most using race fuel in a stock engine use U4. In a properly tuned setup, U4 can provide several HP. Unless you are racing I wouldn't be springing the $$$ for U4 all the time.