I have a 1.8 Zafira and its okay on fuel around town. On the motorway its not too bad but it revs high in 5th when cruising. 44mpg is quite possible out of a 2.2 on the mway but I would think that the F23 ratios on the Zafira are different to the F23 in the Vectra.
There is no chance of breaking 28mpg around town unless its a diesel.