If you buy a branded product like caltex, Shell, FUCHS, etc, you are buying into quality - a good filter and a proper temperature engine with 3 litre sump for approx till 1000cc displacement engine will easily run the oil to 5000 kms.
If your engine is really sloppy and is running stone cold with blocked breather on trash oil filter then even using a full gp IV synthetic will not do any miracles.