It is necessary to lower the fule pressure or you will be pig rich. Running high fuel pressure causes injectors to work very hard which in turns heats the fuel. Say it with me guys - heat causes detonation. Running larger injectors allows for lower pressure levels and much happier injectors. It is generally accepted that larger injectors allows for more timing. You have to find the trade off between idle, driveability, mpg, and size. I am a believer in run as big as you can which is why I have 625's and stock fuel pressure levels. :)

I think Corbins page has some good info.