I will have to take the S4 one day I thought they were restricted, that is impressive fully loaded.
I totally agree that at 120 its fine, 140 and above it gets very hard work. I think trying to preempt other people changing lanes was the biggest strain. Trying to work out how fast cars are coming up behind you at night isn’t that easy either, I always take it easy on their roads at night but you still get cars coming up at 140+ and have to be incredibly cautious changing lanes.
I hired an M4 last time I was out there and accelerated as I changed lane on a very slightly damp road and could feel the rear and twitching, as was mine at that point, very scary at over 100! It certainly made me a lot more cautious.