I’ve not driven one but I would be pretty certian it will be perfectly fine. I say this because I used to have a MK1 Focus with at 1.8l Zetec normally aspirated engine. Nowhere near 125HP, or the torque, but it handled many a 350mile mostly motorway family trip to the southwest with no problems at all at typcial real-world motorways speeds. It didn’t have blistering accellaration by any stretch (i’d expect the ecoboost to be better there), but easily handled typical motorway speeds.
Just because it’s a small engine don’t think its going to be ‘stressed’ and unreliable. I’m sure the engineers have designed the stress levels to be well within what is required for a perfectly reliable engine capable of many hundred of thousands of miles. Managing stress in mechanical parts is a basic and fundamental part of design engieering. And at the end of the day 125bhp is not alot at all in the grand scheme of things and well within the capabilities of modern materials and engine design. Look at one of the worlds most reliable enignes – the Honda Vtec in the Type R’s – twice the capacity, twice the power, another few thousand RPM red line capability (alot more challenging from an engineering viewpoint) and no engine is more reliable.
I recently had a new Focus as a hire car and it is easily as good, if not better than any of its competition (i’ve pretty much driven them all as hire cars over the last year or two) – it certainly drove better than the rest of them, certainly anything out of the VAG stable – in fact i’d say its closes rival is the Hyundai i30!!