EC 4+2 means you need 4 out of 6 chunks of the object or parity to retrieve the object. This means in a worst case scenario you could withstand 2 nodes failing and still retrieve your objects. The more nodes you have, the more chances you have that you could loose more than 2 nodes and still have the minimum 4 chunks of every object, but there is no guarantee.
With EC4+1, you still require 4 chunks of the object or parity to retrieve the object. With only 1 parity chunk, you are protected against loosing 1 node for sure, and again depending on the number of nodes you might be able to survive more than 1 node data loss but no guarantee.