so far i have used ron 95/97 petrol full tank vs ron 92 FULL TANK, VS 50-50 mix tanks over full tank till empty blinking fuel tank... all this quite a few times
when on normal petrol, fuel consumption on a fixed daily highway only route at fix speed is slightly higher, points on guage drop a little quicker, since km and speed are constant and time of drive is almost same, so drop of guage points is actually quicker.. almost 1 extra point falls in 2 days vs pure hioctane only.
full hioctane also gives an almost dead silent running engine with almost unfeelable engine vibration. a pure normal petrol gives a slight more vibration on every stop,.. engine noise on sudden pick is also higher in 1st gear with 92.
mixing both didnot give any major feelable difference.. i guess that cz since the difference in extremes isnt too high, the middle point feels negligible.
just personal experience of testing all this over 5000km period.