Occasionally. Normally it's 128kph peak speed but I've occasionally seen my Lakeshore West GOtrain go between 135-140kph, during moments when the train is running slightly late, on a very good sunny day. These speeds have been hit in the long straightaway sections between stations. I used an iPhone GPS speedometer app. And, yes, it did sustain for about 15 seconds, well beyond normal GPS jitter/error, and newer phones are pretty accurate.
For the Georgetown corridor, the station spacing is similiar. The UPX trainset should be able to accelerate faster, being an MMU. However, speed limits will clearly be the limiting factor (including factors such as vertical curvature, etc). UPX should easily be able to accelerate to 140-145kph north of Weston, after the curve. It probably won't happen all the time, and probably only if a train is running late and the track is all-clear, but if MY Lakeshore West GOtrain has occasionally hit almost 140kph between stations, then UPX most certainly can do so north of Weston after the curve. There's more straight railway over there between the Weston curve and the Perason spur, than the moments my Lakeshore West train manages to hit 128kph with less acceleration than the UPX.
