One thing worth mentioning is that the S-04's have NO tread warranty. The Michelin PSS's have a 30,000 miles warranty, which is 50% better than the PS2's.
I don't think you could lose with either. The S-03's are FANTASTIC back in their day and I can't imagine them missing the bar this time around. With the PSS's though, I just can't find a single solitary complaint. They aren't even expensive, the S-04's just happen to cost less.
I'd love to see if that cost is offset by the PSS's over the course of like 4-5 years. I'll bet that the cost benefits don't offset the rate of wear.