Bentley Continental Supersports @ Madeenat Al Bahar probably has fast lap times around 2:15 so a 3 lap QR would probably work best, 4 laps would be pushing 9 minutes race time. It could be open setup (OS) as you can pretty much only change the tire pressure, and this thing is a beast and hard to break so we could go with Damage ON to make things interesting.
The reason I'm asking for the Ariel Atom on an oval is because I don't think I've ever seen it available outside of Practice, but I know the drafting with them is an awesome thing to behold even sub 200mph.
Kentucky would have lap times around and under 30 seconds so 12 laps would come in around a 6 minute race.
Auto Club Speedway would have lap times approaching 35 seconds in a fast draft so a perfect 10 laps would do well here, and would be my preference over Kentucky.
I'm still not sure what the better gear setting would be, 13/50 claims the highest speed but the 13/47 may be fastest in a draft, so (OS) may be a consideration on this as well. But go with the 13/50 if closed.