According to Broughy, who tests vehicle top speed, and lap times by driving them on a track (which takes in the vehicle stats: speed, acceleration, handling, weight, among other stats, into consideration), the current fastest SUV is the Pegassi Toros, with the Lampadati Novak second, and the Übermacht Rebla GTS third.
The fastest SUV by the top speed (game ...
According to this article, which was written around three months before the Cayo Perico update:
1) Pegassi Toros
Top Speed: 127.50 mph (205.19 km/h)
The Pegassi Toros might be one of the most visually impressive SUVs on
this list. It takes inspiration from real-life vehicles such as
Lamborghini Urus, Lamborghini Aventador, and Audi Q8.