Yes, 73 and 74, even though they're "close" on the number scale, have different characteristics. 73 is very clean and very snappy off the spot. Off the top of my head, the Bank Pearl, Break Point Pearl and Dirty Look all have 73 Pearl. Snappy is a good way to describe the last 2, and the Bank Pearl was strong due to the core shape. My Freight Train was stupid strong off the spot, due to the core shape.
Now the .018 difference... You might not see much difference on a house shot, but lower diff will really show its importance on flatter shots and tougher shots. Where the Adrenaline might Jack knife off the end of the pattern, the Encore will not due to the lower diff. And it is significant. Remember, the max diff is .060, so this is a reduction of a 1/3 allowable diff.