mate i do the same full tank and its comes 270 to 300 miles depands how i drive that beast... 2Ltr Zetec might do more miles but u know its aint that fast like ST....

i put optimax once in a month in my ST170 and to be honnest its totally standard i mean NO ENGINE MODS and its on 177.7 BHP and i m well happy...

CheeRS
Ali