I was under the impression from various tuners and people who have dyno'd there cars on here that the Focus actually runs pretty lean from the factory and especially so with bolt-ons. Certainly not too rich.
It's one of the many reasons why people are so mad about waiting for tuning from SCT or whoever the hell finally decides to sell a solution.
I'd link to a specific thread, but at this point I think it's been discussed in like 5 at least haha!
Anyway, just something to consider.