For me the Crown shoots more accurately off the bench, especially when coupled with the new GRS stocks. Even with a Bag Rider on the Impact, I can still achieve significantly more steadiness with the Crown, in its more traditional long rifle format.
I also try to get a gun tuned for smoothness and accuracy with a specific projectile, and then leave it there. While the Crown is a little more difficult to achieve that initial optimal tune (have to remove the action from the stock for fine tuning the hammer spring pre-tension), once I get what I am looking for, I have found the Crowns to have an overall smoother shot cycle (mine are wood stocked, so the extra weight also helps there).
Once again for me, my favorite configuration of the Impact is the Compact model. So handy to carry around, plenty of power and accuracy, great shot count and plenty of practical accuracy for the ground squirrels I am dealing with. But on the bench I will take a similarly configured (same caliber, barrel length, etc) Crown any day of the week for the most precision.