According to Mactracker, the 5400 needs 70ns dimms, and the 5500 needs EDO.  That may be the source of the confusion. Or maybe the overlap in speeds: Mactracker says the 5400 goes up to 200Mhz, and the 5400 starts at 225; but one of the ram places I'm looking at lists 225 as the top end for the 5400, and lists both EDO and non-EDO dimms.  According to their website: "Although FPM is standard, EDO may be used. If you have no preference, choose the least expensive."

Here's their website: http://www.memoryx.com/powermac5400.html

As others have said, 60ns will usually do fine in place of 70 ns.