Marco , , fantastic and concise information as usual .
Ive had both Viscous diffs and quaife diffs in 2wd Sierras now , the viscous i found very predictable up to about 350bhp , then i bought a Quaife unit from TF to cope with a bit more power , it was a bit noisy into corners when it was working and i found it tried to drive you straight off at right hand corners which i didn't like much .
Ive now bought an X-trac plated 9" Diff so i'll let you know how that compares when it gets a run .