Technically, the amount of cloud cover is irrelevant - it should be considered as an overcast, ie 8 okta. How much of a hole in the cloud do you expect to be able to see the runway? And where will that hole be when you reach the minima?
However, most approaches give an RVR minima and not a ceiling mnima. This is because bright appraoch lights can penetrate cloud for a certain distance and that distance will depend on how bright the lights are. However, some operators place a cloud limit on approaches. for example, one operator i have wored for stipulated that ceiling was assessed as 5/8ths or more and another placed a limit on F/Os flying the approach of the cloud ceiling 100' above minima.