most of the stuff I hunt is beyond 400 yards. so calculations and knowledge is very important. so do I calculate velocity, or for Kinetic Energy?

so it was suggested to me by a reputable gun store, to decrease my bullet weight to 120 grns, from 140, and change powder to R-22. follow the recipe that Barnes have so my muzzle velocity would increase to 3450 (book) and add another 60 fps for every inch over 24, therefore 60x3.5 or 210 fps so a total of 3660fps. From my 140 shooting @ 3200 + 210 or 3410. so E= .5MVV or 60 x 13395600. either way, I am led to believe that @ 1000 yards there is still 950+ft/lbs and an extremely flat ballistic 1868 using 120 grn bullets and...less powder. Or the 140 grns, @3410 fps with the same drop, but for some reason less velocity at 1000 yards and more energy at 1100 ft/lbs, and a velocity of 1680 fps. Oh my brain hurts

ok... why?