I am on my second 1.4 and (pre-Covid) regularly did 100 mile trips on Motorway/Dual-Carriageway and both cars have cruised without a hiccup at 70 (I have a sat-nag in the passanger seat). I have not managed to top either of them out, but this seems like the 75% of top speed generally recognised as the designed cruise speed. So I would not worry.
For me there is a minor flat spot when fully loaded around 40-50, but as long as you allow for it it can be dealt with. I am hoping we can get back to a level of normality and get back to making those trips again