i would keep that pump in your car and rewire it. see how it does. jay racing is quality stuff among DSM's, i have never seen anyone use their pumps in a subaru but i am curious as to how they work. if it doesn't work, i will take it back and sell it to some DSM kid on craigslist.
also, to add, we checked voltage at the fuel pump and it was about 12.2 at WOT and mid 13's at cruising. it is possible that it's losing voltage between the actual plug and the pump itself. never done a rewire kit, so i don't know.