The Whitworth was capable of striking a white painted oak 32' x 2' target at 1880 yards. Not only would it strike it, it would penetrate deeply into the oak. The size of the target represented a formation of men standing shoulder to shoulder.
Whitworths may be seen today at:
Tennessee State Museum, Nashville, TN.
45th Infantry Division, Thunderbird Museum (Oklahoma City, OK). This one has Confederate provenance and can be traced to the soldier who carried it. His photo is displayed with the rifle.
I think there are Whitworths at (haven't been to these places in years):
Chickamauga National Battlefield Park
Gettysburg National Battlefield Park
Virginia Historical Society
ETA: When the Confederates abandoned Morris Island to the Union forces, they took their Whitworths to Fort Sumter and from there hit Union soliders at over 1300 yards distance.