Well mate it's okay for you to drive at any speeds but below 100 ideally on a brand new engine. Just make sure you don't start by full throttle after you warm up your engine. My dad did the same thing on his brand new Mitsubishi Galant you did on ford fiesta. The result was that after the first 1000km check-up, the sound of the engine was like a small pick-up truck engine!!! I was shocked, because the sound was coming all the time, so i did some research on how and why the sound was coming, from there onwards i got my interest of Mechanical Engineering, so came to know from books and other sources that when your engine is new, all the moving parts inside the block needs to sustain a reasonable amount of heat for them to get the coat and than risist. Which in the long run would prove ideal. So when you drive a new engine on 140kms! certainly the parts would heat too much, and therefore in hte combustion chamber the piston which moves up and down face minor cracks, and those cracks are the reason behind that truck like sound from the engine which I heard. If the pistons are run enough and than continue after changing new oil, it won't be damaged anymore.
That is why there is a running-in period for the new engines to be completed after you drive on high speeds with full acceleration! And if you see the manuals, for every car there is a running-in period till the 1st check-up. You should always drive smoothly, if you want your car engine's long life.
We had Maxima, before that Accord...and on all the manuals there was in the Maintenance section, its clearly mentioned: don't tow anything with the car, don't use full throttle, and don't drive more than 1/5th of the top speed. Even for my new Ibiza its there in the manual, my car is hardly 127kms now
its just my opinion mate, so its upto you how you wanna drive, so nothing personal mate
cheers.