I've been running 91 octane and swear the GDI engine runs more powerfully and with no "pinging" sound that I get running regular. Has anyone else experienced this?

2103 Hyundai Accent SE 127,000ish miles

 

There are additives and refining of premium will do a better job of reducing carbon deposits. An occasional tankful will never hurt and will help clean up some deposits.
Fuel injected engines are not supposed to require premium fuel, but a load of premium every couple tankfuls does have some benefits.