NGV's cheaper.

Fuel or engine oil?
If fuel then please dun pick Shell. Might save but no performance.

The key point for low FC is your right foot. Please click my fuelly, before 16 Dec 2012 fuel up i use 0W30 engine oil, after that is thicker 5W50 oil, FC wise remain almost same.

I can almost concludes that engine oil effect on FC is negligible.

Same also. Dun use Shell.
to your car.
But he want performance. 

seem like you having misunderstanding
waiting someone with better english writing to reply at here 

u can use aircon.. but set at the lowest...

Talk is cheap lemme drive your car we go midnight run. I show u how to get 16km/litre. If want 20km/litre need the grandmaster Luke to demonstrate liao

Today went to EA looking for budget HU around 5xx, but with Bluetooth priority. Asking this asking that, install universal steering adapter module to allow stock steering audio control. End up spended RM950. 
Bought JVC KD-R826BT HU, remain the stock speaker. So far very satisfy with EA workmanship and the different between stock HU and JVC HU audio quality is so obvious. Bass is now stronger, vocal and treble so clear. Tested the bluetooth audio streaming using my Galaxy Note, no jerk, no lag, superb performance.