We run mid grade in our EL. It runs fine on regular but with turbos, the Texas heat and my heavy foot, I just bump it up a bit. I notice no difference in fuel mileage. I have a Jeep Cherokee TH that hangs in third unless you come to a complete stop. If you roll-and-go, it tries to take off in third and as you press the go pedal a bit to much, suddenly lurches into 1st and you swallow your fillings. I'm experienced with delayed downshifting. It's a fine vehicle, otherwise, with the best AWD/4WD system I've ever used, even over the Audi, but now I'm chasing rabbits so back to topic...
On our '15 EL we do not have any issue with delayed downshifting, per-say. Now, if the turbo's aren't spooled and when you're just cruising and you give it the go juice, it will downshift the transmission and then the turbo's spool up giving the effect of a delay but it's actually not. It's just good ol' turbo lag.
I like playing with the manual shiftier and do it quite a bit. In fact my gear selector readout used to just say "D" but now it stays in constant select gear mode from start. I don't know how I made that happen but I like it. Anyway, when I know I'm going to be doing more, let's say, "spirited" driving, I like to drop two gears so the turbos stayed spooled and then there is not issue at all when I want to propel a 6000#, 4WD land yacht through the masses of the road zombies.