Looking at OU, 100 has always been a pretty good base Speed benchmark. Pokemon that are or have been notable in older gens of OU at base 100 Speed include Jirachi, Zapdos, Celebi, Mew, Shaymin, Volcarona, Salamence, Charizard + Megas, Mega Gardevoir, Manaphy, Miltank, Flygon, Tentacuel, Ninetails, and Staraptor. It's a pretty large and relevant group, which is why Pokemon that creep past them (such as the Latis, Terrakion, Keldeo, Gengar, Tauros, Infernape, and even closer cases like Garchomp and Landorus) are viewed as relatively fast / above-average.