W50 is good for older cars where the piston wall bore gap has worn and gap are larger thus require thicker lube. Its also good for cars that run high speed with very hot engine and its good for extreme hot weather (Saudi, etc). For Preve and other newer proton, I doub't we'll ever need 50 weighted lube unless its old.

Even tho its FS, the lube is too thick for balance FC saving and pickup power, so for me, its not worth it to change to weight 50 FS coz the the car will USUALLY be heavier on pickup and does not help in FC in order to reduce 1 service.

oh btw 5W does not mean better startup. There is no difference in 0W, 5W and 10W as it is winter rating, sub zero temperature, so 10W will act the same as 5W in our morning startup.