I noticed a significant difference with 906s - although my 99 talls and 4600s were a bit beat.
Unless you are running air bags to assist with load, it's an engineering challenge having an unladen softly sprung vehicle capable of handling significant payload. I was also able to slightly compress my 99 talls with my hands while the 906s were as stiff as concrete.
99 talls have 7 coils compared to 906s which have 9. Spring thickness / diameter of the 906s was a bit larger than the 99 talls.
Logically, 906s should be harsher than 99 talls unless you went to a waaaay softer shock.
