Not everybody will see the same results with premium so it's good to try it out and see if the extra cost matches the miles per gallon since driving styles can wildy very the results.
I've tried it on my 4Runner and there is no gain but with the Focus I'm hoping for the best.
'12 Focus Red Candy SE Sport 5 spd
'99 Toyota 4Runner Sport
'11 Subaru WRX STI Hatch