Basically replacing 2 at a time. I went back with stock OEM and now if another one goes out it will be simple as pie to replace. Save your money and do it right the first time, go back with stock OEM or just upgrade, whichever fits your future needs and budget.
My next step is to do the injector power mod, to cut off power when the key is turned off. I am very happy with my decision to go back stock :) ( for now ) lol