The Lexus will require premium. Using regular in the MKC 2.3 at the moment would save about 10% on fuel costs over premium where I am. To me that makes the equivalent MPG pretty decent, and for the type of driving I do it will probably bring it close to the 24 MPG combined of the NX.
There are a lot of things I like about the NX, but my interest in it has been waning since packaging details were released. What I would consider a fully loaded NX can't be purchased, especially in the US. If you want adaptive variable suspension, the boost meter, or a front profile that isn't a beak you have to buy the F-Sport that doesn't have a bunch of creature comforts available. If you live in the US there's also no 835 Watt sound system, HUD, Surround view parking assistance, or pano roof available. The official 0-60 is the slowest, or close to it, in class.
They also need to get crackin' on a larger turbo now that they've got a small one. Lexus is so concerned about reliability that it takes them eons to come out with these conservative powertrains.