Real world data

Wondering if anybody could help out, got a rem 700 in 7mm rem mag with a 26 in barrel, planning on heading down to the Palmy shoot but haven't shot it long range yet, going to shoot 150 gr factory Winchester which they say muzzle velocity is 3100 fps but ADI have a starting load at 2800 fps the difference being over 10 inch at 600 yards, anybody have any real world date they would like to share?
Thanks

Your rifle will most probably be different to others velocity wise anyway.

last time there was a chronograph available