Its a bit of a waste if your engine hasn't been tuned for it.
I used to use standard 91 in my VP. Because its got the HSV enhanced 180kW motor, its got a knock sensor. I once tried Shell V Power racing when I drove 1000km to Brisbane in it and it made a big difference compared to standard 91. But fuel economy didn't increase, prob made it worse, and when it was $1.50 a litre in Wollongong for V Power racing, I wasn't too keen on filling up with it that often.
I have tried 91-98 in my suzuki grand vitara and there is really no difference to the way it runs.