My policy on putting fuel in is that I use the cheapest stuff that happens to be nearby when the needle's pointing to the red bit on the dial!
I've run quite a variety of cars from a 1.1 205 back in the day through to my ZS's, ZT's a BMW 540i, 4l Soarer, Hilux Surf and even an MG RV8, all on the cheapest fuel (usually supermarket) and never had a problem. With some of those, the 540i most recently I did try high octane fuels and was amazed at the difference..........there simply wasn't any!
The only time I've ever had a fuel related issue was when the entire region had a contaminated batch of LPG which contained too much heavy oil or something which meant that the car would still on idle on gas. Thankfully that problem stopped when the local station refilled their tanks!