I got to test drive a pre-LCI and an LCI within one week of each other. I know this might not be accurate in comparison to long-term use, however the LCI was much softer. For reference, I drive an E63s and the pre-LCI comps were much stiffer then that. The new LCI comps are for sure much more softer than the pre-LCI and the E63s I have.
I had a S63 at one point and that's been the softest super sedan I've drivin. The new LCI M5 comp's comfort is between the comfort of the E63s (pre-facelift) and the S63.
Hope this helps
