I will break your message into three parts
1) Fuel Options: Yes I do mix high octane with normal fuel. Not 50, 50 but 10 liters of Hi Octane (Preferably V Power) and 20 liters of Ron 92 (from shell pump)
2) Buying Air Filter from filter house: Honestly I am not sure about this piece since I am also looking for better air filter for my Non Turbo car. Please refer to earlier post in the same thread.
3) Econ Mode: The problem lies with Air Filter. These turbo cars requires high intake of air and I feel you are using a locally manufactured air filter which I feel is damaging your engine and decreasing the performance. Use original filter and but it from Ganj Mandi if you are in Lahore.
P:S. I bought three locally manufactured air filters and found issues with all of them considering all of them were normal filters and these cars requires carbonized air filter to prevent oil going into engine as well. I infact cleaned my original air filter with the help of petrol and small detergent and honestly it worked for me for 3-4 months. But eventually i have to change it as well.
Let me know if I can help you with additional information.