My car (5 year old Volvo) has never run better.

I've yet to see if there's an economy benefit (I'm sure there will be).

Don't be so sure. It may run smoother and could, with tuning, increase
power, but it does not guarantee better fuel economy. Increasing the octane
actually reduces the energy content of the fuel. It is likely that the
formula has been tweaked to restore this, or very slightly increase it over
standard fuel, but you shouldn't expect a large increase in economy.

Higher octane fuel is generally much worse for the environment, due to the
need for larger quantities of nasty aromatics, like benzene.

Christian.