What are typical max speeds for pro downhill races?
The differences are quite significant from race to race - each track is different. Also events such as Rampage are not too much about speed. The top speed may vary between 55-65km/h on tracks such as Mount Sainte Anne up to around 80km/h in Pietermaritzburg which is known for high speeds achieved. Of course all assuming good weather.

Also these speeds are kept only for a few seconds (in the best case), the average speeds come around 30km/h mark course and weather dependent.