In my experience with my Metal 177, the tail makes the biggest impact while not carving, where it really does make the board easier to ride. Mine serves double duty as my all-mtn board.
While carving, it releases a little easier, and is more forgiving on uneven terrain (slush, chop, piles, etc). Does it make me pine for a rounded tail on my other carving boards? No.
Comparing the Metal 187 to that Coiler isn't really apples to apples. The Coiler is also going to have a much shorter nose, which is a different issue altogether. The running length of the Metal Priors is the same as the corresponding WCRs. The Metals are just 2cm longer overall. The benefit of the shape is significant, the penalty of the extra weight is not.
This doesn't apply to you Jeff, but I've taught my father how to carve, my wife how to snowboard (in hardboots from day one), and helped my sister make the transition to hardboots. For all of them, a round tail made a world of difference. My dad started on an FP, my sister on an Alp, and my wife on a Stat. Switching them all to E-decks opened the door to the next level.
ps - no dare needed.