OK so my OCD kicked in LOL.
Jeep JK Unlimited - inside and out with 4, tailgate, doors no top ~ 204 (204/10 gallons = 20.4sq ft to the gallon)
240Z - inside and out 2 doors, hatch, roof & hood. ~ 147 (147/20.4 = 7.2 gallons)
So educated guess the Z would need 7.2 gallons of SC/Ceramic Lizardskin combined to get the same deadening. I layed it down pretty thick on that Jeep. I think you are headed in the right direction with the Dynamat.
Any news on the paint?