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I have found that on unrestricted sections of the German autobahns, my Mk5 GTI can cruise happily all day at around 125 mph but then acceleration gets very slow upwards to 145 mph (accurate GPS speedo). Hatchback aerodynamics are not great at the higher speeds.
180 mph in Audi RS6 Avant, Porsche, Mercedes, BMW, etc autobahn-stormers is quite common and not a problem if you are driving as you should be.... FOCUSSED!!