Most of the DME ARCS here in the US are within 10 miles of so of the FAF and the point where you would intercept the ARC at the IAF would dictate that you be down around flaps 5 in a B777, and somewhere roughly around 180Kts. If your going to be doing a VNAV approach with this ARC transition you need to get some flaps out for the "on approach logic" to kick in. I don't how anyone would do this approach maneuver clean, much less at 250kts?