Back when my R31 was running good, I got an extra 50km from 55L fill up switching from Shell 91 to Mobil 91. All highway driving, same condition and driving style (I drove to Sydney to Kiama and back, two days back to back).
I put Caltex E10 (the only one they had) in the R31, it would stall on cold starts and ran a tad rough. Didn't do any testing with that fuel as I went straight back to Mobil for many years of happy motoring.
Used BP 98 a few times, ran the same as Mobil, but they generally are more expensive so no point using BP.