These films, like Ektachrome 1600 are DX coded to the EI that is on the box. To get this speed they must be push processed.(posted 8780 days ago)In fact, if you look at the box, it states the number as an EI not an ISO.
With some/many of these films, there are differences that make them more suitable for push processing. Mainly starting off lower in contrast, so that when pushed the contrast gain doesn' get out of control.