amon458, you dont lose/gain that much, its usually closer to 50fps per inch in my experience. however 50fps can make a big difference when your throwing 500+ grains of lead at something.
buster95, i suppose its possible to get 2200fps with a 26 inch barrel but you would need to load the cartridge fairly hot. i believe 2100-2150 would be more of a normal speed with that barrel length. Hornady loads their factory DGX/DGS 458 WM ammunition very hot, in fact most factory 458 WM ammunition ive seen showed pressure signs after being fired.
-matt