A progressive coil will typically have a softer ride. It takes less weight/pressure to compress the close wraps of the progressive coil. Then with more pressure the wider space wraps will compress.
FYI: the TRDs are ~595# spring rate and the 881 are 550#
The height and the number of wraps effects the way the coils handle the weight applied. It's hard to directly compare the spring rates of a progressive and non-progressive coil.