Top speed needs a lot of space, i remember doing it on german autobahn and like 50km were gone before i knew it. To be honest at those speeds i was rather concentrated on the road ahead and nothing else..
With a 3.2l 6-speed euro coupe, full stock engine, R wing and hood and popups, went up to almost 290km/h. There's more to get with better flowing exhaust, and i didnt tape the A/C radiator openings.
From 275km/h and upwards it accelerates quite slowly but it does, hence the lot of space needed.