Here in Australia the Focus uses the same 2 Liter GDI engine. However, all performance figures supplied by Ford here for the Focus, are explicitly stated as being in relation to Premium gas (the USA equivalent of 91 Octane).
In other words, the recommended fuel for the Focus is 91-98 RON (87-94 in USA) and I've read elsewhere that while it will run on regular, Premium is preferred.
The engine is rated in the USA at 120 kW (160 HP) and that's on regular. Here, the engine is rated at 125 kW (167 HP), but that's on Premium. No figures are available here for Regular.
It could be that the car is tuned differently here - I wouldn't know. However, the implication is that Premium gives an extra 7 HP.