You can’t really determine how fast a car will be simply from its body style. However, as a generalised guide, coupes tend to be slightly lighter and more aerodynamic than an equivalent saloon model so, in many cases, can be faster than their four-door siblings. This effect is even more exaggerated when comparing coupes to SUVs.
Plus, most carmakers tend to sell coupes with the more powerful engine options in a vehicle lineup, meaning coupes are often equipped with more horsepower as standard compared with similar saloon models.