thanks for the reply guys so it seems like if im doing short oci of 5000km then the cheapest full synthetic that i can find is good enough for me and the expensiver oils wont have any beneift in the short oci. but if i want longer oci then for sure the expensive oils are worth it??
No that's not really what's being said.
What I, and others are saying is that any oil that meets the vehicle manufacture's specifications will work for your particular vehicle. While there are a number of high priced oils available to you, you aren't necessarily gaining anything from them when you run them throughout the manufacturer's specified oil change interval. This has to do with the quality of today's oil and the fact that any oil carrying the specified certifications must meet minimum requirements. That's a pretty narrow window by the way.
If you do a bit of reading here on BITOG you'll find this in spades. Most people here run the cheapest oil they can find as long as it meets their vehicle specifications. Sometimes that means they're running Wal-Mart brand, or a house brand synthetic blend, or they picked up a name brand full synthetic while it was on sale with a rebate.
In terms of when you should change the oil, most here find 8000 km (5000 miles) to be a short oil change interval with many extending it to 16,000 km (10,000 miles) on a healthy engine. This is with a number of different synthetic blend and full synthetic oils. Yes there will be other factors involved such as your driving habits, or if you have turbo direct gas injection motor etc., but for the most part the oils will stand up to much longer intervals and provide similar wear results in your engine.
Have a look at the article I posted. It's based on actual oil analysis results and it demonstrates that there's very little difference in wear between the lower priced oil vs. high end full synthetics over similar oil change intervals.