Luca did his 183.9 with 480bhp with 626bhp Martin managed 194.7 that tells you what you should pull, certainly over 190mph. All sounds simple but that Power must be available after 30secs of 100% throttle.
Ford quote cd of .295 for the Focus better than a Saff so unless you are hoisting a sail on the roof it will pull those speeds.

We have found you can pull a few hundred rpm past peak Power so gear for say 190 at that & if you have 600bhp you will reach it first run.
Remember you can have an engine that revs to 15k but if it has peak Power at 7k & falls away it wont pull much more than that before you hit the aero wall.