I have a nice 2 lightning skills 20fc Amu so I can use Ormus' Robes on my Nova Sorc. Is this useful or is Skin of the Vipermagi better due to better resistances?

Lite mastery gives % increase, so ormus small % increase is barely noticed. Skin also has 13 mdr which is actually a large number for a 95/.75 es sorc. I guess if you use the cyclone armor the mdr isn't as noticeable, but still there really isn't a need to swap.

Cyclone armor from info is not viavle to use. Its calculated before ES, so in practice its gone on seconda and you would need to recast it like every 15sec