unless you plan on continuing training in speed feed it tomato berries to erase the speed EV's (also read http://www.serebii.net/games/evs.shtml for a better explanation than i could give lol)
ok well the main reason you not getting alot is that cubones base speed is only 35 meaning that with an adamant nature its max can only be 169 as a cubone(thats if it has flawless IV's) or 189 as a marowak