So after a Mon-Fri test drive (lease company) in an NX300h FSport 400 miles of motorway, A, B and smaller road I managed 36.9 mpg according to the trip computer (yes I know not as accurate as brim to brim but I'm not that anal). I was being very careful but making good progress, 75-80 on the mway and speed limit elsewhere. Lovely driving position, great headlights (unlike my FSport IS), and just a nice place to be. I did sit in a Luxury though and prefer the seats in that' although I've always had sports seats, maybe I'm getting old.
Anyway back in my IS300h FSport today and averaging 43 mpg and not hanging around over similar routes. Hope this helps.
I went into the Lexus dealer this week, where I looked at the luxury model, actually to confirm if a roof rack can be fitted with the panoramic roof. Comments on this forum say not and I tend to believe the forum over dealers. The dealer inevitably reckoned it was possible but is actually going to order some in and try them!
Hope this helps.