Havin done both i would say this was harder than the SDW for a few good reasons.
(a) Running on the flat for all that time using the same muscle groups is a killer on the legs.
(b) The temptation to go off too fast is hard to resist as the trail at the beginning is so runable.
(c) The night section is bleak and a total head f**k
(d) The last 15/20 mile is a horrible rutted trail.
All adds to the fun tho and i can't wait.