2017 Cascada, using 87 Octane, got 30.0 MPG doing a steady 72 mph on the cruise control for 250 plus miles. (Top up, and no significant wind)
Next tank , ran 93 octane, and the mpg only improved to 32.1 (all other conditions the same).
IMHO, the extra 20% or so that 93 octane cost, was not worth it to just get a 7% improvement in mpg. (The owners manual, although recommending 93 octane, does state that 87 can be used, but expect lower mpg and performance.)
How about others out there?