I don't know about the slingshot since i don't yet have one(grrrr) but for all my other vehicles and bikes i will always use premium(heck even my riding mower/snowblower use it) it has never been about performance but about the fact that it will keep the injectors cleaner while also providing a better MPG( if that is even a thing on a sport car/suv), I am also quite adamant about certain brands of gasoline being better than others(Mobil,Costco,BP) = good. SuperAmerica,Freedom,random Mom&Pops = bad
For example i have tracked the miles of almost all our vehicles using Fuelly - Track and Compare your MPG and based on the data Superamerica has the worst possible gas in the state of MN(consitently 2-3 MPG less than costco which is my preferred brand due to convenicence).
For my boat there is a 3-5MPG difference between getting gas a the local river station vs bringing my own from costco.
I am also one of those that firmly believes that not all brands of fluids are created equal and that synthetics needs to go on EVERY darn possible thing(Mobil Fluids on everything).
also given the fact that prices are so close between "cheap gas and premium gas" it is just irresponsible not to go for the good stuff, in my opinion is cheap insurance, kind of like waxing your car/s during winter to protect the finish from salt damage here in the northern states.