I would say to only use Inj Calc's for a reference. What I mean by that is bigger can be better,,, but only if the injector is of very good quality.
You wan the car to idle well and you want to make good power. This requires that the injector cover a lot of ground, in PW. So you want very good control at very low PW's, for idle quality, and predictable flow at high PW's, for power.
That means you want to go with something that is either proven on a Focus (duratec by the sounds of it) or something that is well documented (which from what I hear Delphi is near the top of the heap).
So what I say to do is look for a an injector that flows well at very low PW's, is well documented and is still big enough to fit your power goals ... and try to go with the newest design possible, which in your case means that if it requires an adapter / it's not for you, stick with an EV6 style injector. Which is to say, you are doing the correct thing by selling the current 42# EV1 injectors you have.