you can search duty and custom calculator for punjab pakistan. but to be accurate you should call any custom clearance agent who deals in clearing cars, with C&F price of the vehicle reached on the port? the agent will give you the accurate cost including all the payments you need to pay to the gov and the agent.
rest as far as GTR and Nismo is concerned its the same thing as Toyota supra and TRD. GTR is a brand name for the nissan's skyline. like a model of the car. now they only have a GTR in skyline, before the R35 they used to have more than one variant of it. like GTS-t, GTS and GTR. but in R35 they only have a GTR model. NISMO (NISsan MOtorsoprts) is a division of Nissan where they have cars specially to compete in worldwide racing events. same as Toyota have racing cars and have a division which they call TRD( Toyota Racing Development). so basicaly to answer your question in simple words GTR is a racing car and Nismo is a official racing division/department of Nissan worldwide.
regards,
Ali shehzad