It depends on how you use the car. If you are feather light on the throttle, then aye, perhaps paying that bit extra will pay dividends in regards to mpg.
If you are like a wannabe F1 driver, then no, it won't.
Undoubtedly there are going to be people that come on here a bit later, and claim the world of how 97+ Ron has unleased a gazillion horsepower from their engine. I would call it a more placebo effect, especially after playing with fuel RON ratings over the last few years.
As I said, if it's put in yours then the engine will retard* the timing of SOI which will save you fuel, as it will not need as much to enact the same burn, it will burn cleaner, and maybe just maybe unleash a couple of ponies, but only at the top end of the scale.
*Edit: I re-read this and to make it clear - In terms of retarding, that is retarding back to the TDC from the SOI generally SOI is measured in negative degrees so if SOI is 4BTDC retarding it will bring it to 2BTDC.
** TDC - TOP DEAD CENTRE
SOI - START OF INJECTION
BTDC - BEFORE TOP DEAD CENTRE
