i "heard" that the rails are good till about 500 horse, so don't bother upgrading them yet, specially with 30 pounders. on www.turbomustangs.com guys are runnin stock rails with 42 pounders with boost, so you should be fine. Looks cooler to get new ones though.
Lee
The rails are good for 600hp, the fuel lines however create a supply problem with bigger injectors such as 42lb or bigger. Anything bigger than 42lb you should get bigger rails b/c a bigger injector will dry out a stock rail.