Looking on ebay I saw a hi flow fuel rail for the rx8. It states a larger inside diameter than stock and says the mm . Says for top feed injectors, its 80$...

is there anytime point in this is your n/a wth no2.?

 

There is no point in upgrading the rail on an NA 8. Or really on any RX8 actually.

 

The only reason to upgrade the fuel rail is if you were doing a return style system. KG parts already has one made for this very application.
That said I don't think the bore of the stock fuel rail has any ever been suspect of being restrictive, so why do it?