The main issue I have had with the sunroof is the vibrations at highway speed, but it's not that bad compared to wind noise. The car is fairly quiet compared to most at highway speed in this class.
Fuel economy on these cars leaves much to be desired - I kind of wish they offered a 5.0L hybrid option. City driving is terrible
The sunroof has just started to rattle a bit while closed when the temps drop to near freezing. Not always, but sometimes. It has always operated properly. The natural light and airy feeling the roof provides makes up for a bit of rattle in my opinion.
but highway I've gotten up to 8.7L/100 km at 114 km/h.
These cars don't seem to be very expensive to insure.
One drawback is the lower profile tires tend to be more vulnerable to potholes. Replacement is costly, although I got the stock 275 tires in the rear at $200 CAD + tax a pop, so maybe not terrible. The rear tires tend to go a lot faster and you cannot rotate them front to back since they are staggered.
The Lexus GS
I checked on the GS 350 - apparently (at least where I live in Ontario), it costs a lot more to insure the GS 350; so it actually came out to a savings even though the GS would use less fuel. The GS has its drawbacks too - the infotainment UI is a lot worse (although side by side the Mark Levinson audio is a bit better the Lexicon on the audio system) and I found it louder on the highway.
I would advise getting an RWD GS450H for Canada, except for maybe BC residents.
The GS handles better, but the Genesis rides more comfortably and is a larger car.
Maintenance may very well favor the Genesis since you can take them to Hyundai dealers. The other is that the F Sport GS has very costly brake rotor replacement costs.
The F Sport too has lower profile tires.
It looks like cost to own/run is important to you. If so, you should consider the 3.8 - 95% of the time the 5.0 isnt needed. It's better on gas, easier to work on (more room) and has cheaper tires. (18" vs 19"+width).
Oil changes are annoying (not difficult) if you have to do it from underneath - 2 huge aero panels block off the underside. 25k seems like a good deal but condition of the car is important.
You could always go with all 4 tires as 245 - 40 - 19 - I'm thinking about going with all 4 tires as 19 x 9.0 inch wheels and probably something that size for next time I swap my tires.
I agree though that overall cost to own is lower on the 3.8L and possibly the 3.3T, although the 3.3T is somewhere in between and the risk of a turbo failure is always possible.
The other advantage of the 3.8L is that regular fuel is recommended. Premium for the 5.0L.