Even though the P85 only has 15% more HP than the S85, going from a 0-60mph time of 5.4 down to 4.2 requires a ~28.54% higher acceleration. So you'll be feeling a ~25% higher force on your body with the P85 over the S85. See if that's worth $10,000 for you.
I've never ridden in a S before, but...