I would never disagree with the Quiz Master but as suggested there are many claims to this record but the official FIA approved record is Montoya at Monza with a 231.5 mph
Top speeds are in practice limited by the longest straight at the track, in testing one month prior to the 2005 Italian Grand Prix, Juan Pablo Montoya of the McLaren-Mercedes F1 team recorded a record top speed of 372.6 km/h (231.5 mph), which got officially recognised by the FIA as the fastest speed ever achieved by an F1 car, even though it was not set during an officially sanctioned session during a race weekend.
In the 2005 Italian GP Kimi Räikkönen of Mclaren-Mercedes was recorded at 370.1 km/h (229.9 mph). This record was broken at the 2016 Mexican Grand Prix by Williams driver Valtteri Bottas, whose top speed in race conditions was 372.54 km/h (231.48 mph). However, even though this information was shown in FIA's official monitors, the FIA is yet to accept it as an official record. Bottas had previously set an even higher record top speed during qualifying for the 2016 European Grand Prix, recording a speed of 378.035 km/h (234.9 mph), albeit through the use of slipstream drafting. This top speed is yet to be confirmed by any official method as currently the only source of this information is the Williams team's Twitter post, while the FIA's official speed trap data measured Bottas' speed at 366.1 kmh in that instance.
But as I previously suggested the actual fastest speed by a F1 car was Honda which set an FIA ratified record of 400 km/h (249 mph) on a one way run on 21 July 2006 at Bonneville Speedway.
I'm off to hide in a dark corner to avoid any abuse