You need to get a tune either way, im guessing 10.5 on lower octane and 12 to 1 CR on premium. every car will run a little differently depending on engine wear, factory timing, spark plugs,ect.
but you have an automatic station wagon.....so.. you probably shouldn't waste your money if you want to go faster. If you want to go fast for cheap, find a used turbo car for 5 grand. 240sx 300HP rear wheel drive monstor,