I managed to calculate the distance between two points (from two different feature classes) using the vincenty module from geopy.distance.
For quite some time I struggled to find out why I got wrong distances. (even to realize it took me some time)
In the end I figured that the vincenty module requires the coordinates in Latitude/Longitude while the coordinates as they are stored in the feature class shape@xy are stored as Longitude/Langitude.
Can someone confirm this? It doesn't make any sense to me why the vincenty module should require the coordinates the "wrong way" but I only get correct measures when using the coordinates switched to Latitude/Longitude...