Hi GH1,
Since you are looking at numbers to determine costs, other than velocity there will also be trajectory and energy changes. The trajectory I can't give hard numbers on, but your point blank range will be reduced to around 70 yards. Since you hunt heavy cover this may not be a factor. That leaves energy (ft.lbs.). This you will likely notice first. If you are shooting cast bullets, and shoot only broadside or slightly angling shots you will be fine. If you tend to shoot moving, raking and hard quartering shots it might be an issue. Your load at 1,275 gives a muzzle energy of 1,462 ft lbs. If you reduce your velocity to 1,000 fps your muzzle energy drops to 900 ft lbs. This puts you into .44 magnum pistol ranges. Yes this will easily kill deer, but shot placement is the key. You will need to re-learn the trajectory, and be more picky about your shots.