@OP...your post gives the impression that you purchase your engine oil in the following fashion:
At evening time you drive all the way to tel walay ki dukaan...and roll down your window and say:
"3 kilo ZIC de do bhai"
"4 kilo Shell de do"..
"3 kilo caltex de do"
"achi quality wala tel dena meray bhai"
(am i wrong ??)
i mean why not ask for the vehicle's manufacturer's recommended oil GRADE & VISCOSITY ?? Why put all the emphasis on BRAND of oil ?? Every brand comes up with the whole range of oil grades.