MP4.2+6.0

I can only speculate on a bunch of factors here--the D4 generation, later W12 (FSI), 3.0T vs later W12 choice, Saudi climate, etc.

I owned a 2006 D3 W12. That was a 6.0L port injection motor. D4 motor was enlarged to 6.3L, power moved up marginally, direct injection, and different body. D3 had heat soak as they aged. Unclear if it will prove out on D4. I saw it in the 7 to 10 year window and most after 75K miles, so some D4's are just entering that window. Upping the power would not help, but using the 8 speed tranny (6 speed on D3) means engine mostly runs at lower RPM's. If D4 has auto start, that may help too. Further, I think they moved the forward firewall farther away from motor or made it two piece/removable with D4. On D3 W12 motor was just and inch or two (25-50mm) away in some key sensors in back, so sort of a set up already prone to heat soak. A lot of the lows mileage and probably heat seemed more at or near idle while stopped or in traffic. While supercharged, just based on relative power, figure 3.0T may only throw out 60% or so of the heat. Both motors relatively well regarded durability wise as far as I know.

Not aware so much of heat soak on 4.2. I drove a 5 speed (thus often higher RPM's) C5 2000 A6 4.2 though 110K plus miles, then it stayed in family another 75K or so miles. But our San Francisco Bay Area climate is probably a lot milder. 80-90F is common in summer, with it rarely going to 100F. In Central Valley where I would drive it and W12 through maybe 5 times a year, you could see 90F to as high as 110F in summer. If you are seeing heat soak already, that may suggest smaller motor in general. Again, stop start might help some too. I'm not a fan of it in general, but for both fuel economy and motor heat--at least in traffic--it might have this side benefit. The late D4 W12's also had partial cylinder shutdown ("cylinder on demand"/COD) that was a pretty cool set up technically. My 2015 S8 4.0T has it too, but a somewhat less sophisticated implementation--W12 actually rotates among which cylinders are shut down over the times it is engaged.