If you are using a 93 octane tune on you tuner and want to leave it with that tune then you only need the top grade fuel which at around
3000 elevation changes to 91 octane.
93 octane at sea level is the same fuel
at lets say 3500 ft but only registers at 91 octane.
90 octane at sea level is the same fuel at lets say 3500 ft but only registers at 87 octane.
87 octane at sea level is the same fuel at lets say 3500 ft but only registers at 85 octane.
High grade "Premium" fuel is 91 here at 4500 ft.
Midgrade "Med" fuel is 87 octane here at 4500 ft.
low grade "Low" fuel is 85 octane here at 4500 ft.
If you are looking at grades on line, well some people call the best fuel Premium or Super, so it could be terminology issue. The numbers change because of altitude, not because the fuel is different
and Denver has all 3 types so don't worry. In reality it's all about Government laws and Regulations that have to have a standard, that standard is at sea level, so the numbers are bigger but atmosphere psi's up here is lower then down there and that changes the number.