Our driving conditions qualify as "harsh" because of the dustier atmosphere, hotter temps, and the stop-and-go driving brought about by our traffic conditions... thus, i feel more comfy with changing oil every 5K (using mineral oil)... I've seen several cars using synth and extending the drain interval and the results werent really that nice (the oil became dirty sludge).

I guess the best would be to follow what the factory recommends in the manual/service booklet as Pajerokid mentioned.