In the 10 years of driving I've done, I filled up twice out of necessity with Caltex. Once back when E10 was being pushed, caused my R31 to stall when cold and ran like shit (yes, E10), obviously burned through the fuel. Switched to Mobil (regular 91), no issues. Floated between Mobil and Shell, got extra 50km from a tank of 50L from Mobil lol (highway driving SW Sydney to Kiama and back). Even tried Mobil E10, same performance as regular but slightly less mileage.
Seat of pants (no knock sensor readings or anything), my cars always liked Mobil fuels. BP is fine but usually more expensive, so don't bother. Plus Mobil is closest to where I lived (and live), and either on par or cheaper than Caltex. Win win.
Brother's experience: Holden Cruze 1.4 turbo 6spd auto, Caltex E10 to Mobil E10, Mobil got extra 20-30km from his normal driving and 'ran better'. Same shit on 2014 Corolla 1.8L 4spd auto.
I've also advised a handful of non-car friends to switch away from Caltex, but they were too random with filling up 'whatever unleaded fuel' they could find. I did have one comment that switching away from Woolworths led to small but noticeable increase in performance but mileage was the same.
But who cares about real world experiences right?
Mobil fuel comes from the same place as the other brands, out of the ground. What's your point? They use the same depot? They're all the same fuel?