i had the same prob with the rb25.
boost leak-maybe but it should misfire all the time not at higher rpms...is the misfire getting worse or staying the same
coil packs-are you sure you swaped with good ones
spark plugs-can always use new ones
i would def try to change the plugs first unless you have good coil packs that you know are good.
my main prob was the coil packs along with the plugs and the boost leak