speaker effiency

hello can someone please tell why speakers with the same effiency, mind you different in that one is 4 ohm the other 8 ohm, that one would play loader then the other.the one that is 4ohm (thiel cs1.2 )is the one that plays loader. the other is gershman x-1.also next week i am adding the sw-1 sub.it is a passive sub.it has the same effiency as the others 87 or 88.my amp is ocm 200 (100 wpc ).will it get worse (if that's the word )