A 3" MAF tube will be fine for up to about 12psi on the 2.0 duratec, after that you'll basically be at the voltage peak and need a MAFia. Of course that is 12psi with my setup, not necessarily yours. It will be up to you to log the MAF voltage and determine if you need a MAFia.
'04 Mach 1. Built. Turbo. 667whp/631wtq
'06 Focus. Built. Turbo. WMI. (sold)
'03 Mach 1 : 12.61 @ 106.59 (sold)