I don’t think “longest” necessarily means most vertical right? If not then by total miles my favorite long descents are Hermosa Creek Trail(Durango, CO) = about 22 miles and The Whole Enchilada(MOAB, UT) = about 33 miles. Pikes Peak may have a lot of vertical, but the longest trail in Pikes Peak is the Barr Trail which is only about 12 miles in length.