The 1.0 TSI (higher powered one) pulls 2500 rpm @ 70mph. There was another forum member who had the lower powered TSI who mentioned the car could do 57-58mpg on highway runs. Me personally most highway runs at 65-70mph gave me low to mid 50s mpg. My best ever was 57mpg from London to Manchester, starting on 40-50mph roads for the 10-20 miles or so, then the rest were on motorway speeds. One on motorway the car was set on cruise control for 90% of the motorway journey at 68mph. As other members mentioned, its really quiet, the wind the road noise will be more intrusive than engine. I usually drive just below that speed. Later that week, journey from Manchester to Liverpool, going slowly (62-65mph) I got around 60mpg before I started slowing down and hitting some traffic. If it helps...check here:
https://www.autoexpress.co.uk/volkswagen/polo/102737/volkswagen-polo-vs-ford-fiesta-vs-seat-ibiza 2/3 down the page..says it pulls 2.5k rpm @ 70mph...
For comparison, my Leon 2.0TDI 6speed DSG revs @ 2200 rpm @ 70mph, and my current Volvo V40 1.5T petrol 6 speed auto, revs @ 2-2100 rpm @ 70mph.