The S04s consistently rate toward the top of the heap in that summer performance tire category, and they're cheaper than the RE970AS. The S04s are a better deal IMHO unless you're looking for a slightly better all-season tire or looking for a better wear rating. Note that you will sacrifice some performance for those two things. The better wear rating may offset the fact that they're more expensive, but not the performance difference IMHO. If I were going to try to drive the car year 'round here in Minnesota, I'd have sumer tires and dedicated snow tires like Blizzaks, not try to get by on a tire that is going to come with compromises in either season.
http://www.tirerack.com/tires/CompareTires.jsp