The 2.5 will present many problems for focus owners, as the cylinder head has VTC for both the intake and exhasut cams, as well as a second oil pressure port that the 2.0 and 2.3 don't have. Also don't forget that there aren't many manufactures who produce internal parts for the 2.5 since it is still in its infancy.
If power is what you're looking for, then I'd say get a 2.3 built with forged internals and slap a turbo on it. You'll be making more power than any other car sold by Ford. [cool]
BTW I will be doing a 2.3 swap into my 09' soon. From what I have found, the main things that need to be changed are the serpentine belt, passenger mount (or use washers to raise it .5"), oil dipstick needs a hole drilled .5" higher, and the intake cam needs to be swapped out for the 08+ style. everything else such as sensors, IM, exhaust manicat, etc you'll pretty much take from your 2.0 and swap over to the 2.3.