I ride 39 miles to work on 50mph highways, pretty much pegged the hole ride with a handfull of stop lights. Haven't had any problems, around 100mpg but haven't checked in the last 500 milesI know of two Z125's that run like this with more than 800 miles each with no issues.
28 mile round trip to work, doin 55 plus the whole way.
I've rode 170 miles with it pretty much pegged the whole day with no issues. There was actually another Z125 with me, no issues with it either. Tip: Try to stay close behind a pick-up truck, SUV or semi when on 55 mph roads. The drafting effect will allow you to consistently keep the bike above 60 mph.
I'm doing hard break-in on mine and oil change soon. My first tank at one bar left I filled up. Only put 103 miles on it at that point. On my second tank now with 177 miles and only used one bar so far. I ride around in your rev range most times just keeping up with traffic or on the hillsMy first fill up, I averaged a disappointing 60.6 MPG and haven't even been getting into it much, I've been short shifting around 7,000 RPM with occasional runs up to 9,000 RPM. Given, I'm 6'3 and 260 lbs, I wasn't expecting 130 MPG but was expecting to get better MPG than I get on my WR250R.
Also, the fastest indicated speed I have ever seen on this bike was 57 MPH, which was downhill with a 15 MPH tail wind.