For GO, this is past the "pilot" stage and is now an official route. The Toronto <-> London portion was also the route of Amtrak's International, and speed on this section was one of the many "nails in its coffin". The viability of the current train was discussed in another thread when the route was rolled out. Apparently the ridership is exceeding what were very low expectations, with the only major criticism being lack of food and beverage on a 4-hour trip. (GO is looking into this.) It is cheaper than the VIA service on the same route and the drive on the 401 highway is bad - particularly during rush hours - due to massive construction projects and resulting lane closures expected to continue for up to 2 years.Reviving a 4-year-dead thread...
GO Transit's pilot service extension of their Toronto-Kitchener line to London takes over 4 hours total. This might be the longest single-seat commuter train ride in North America, and certainly close to it if not! Most of the extended portion seems to go no faster than 30 mph according to historical data (see for example Intercity Rail Map).
VIA Rail also operates it (Toronto-London-Sarnia) once a day, and the Toronto-London portion is 1.5-2 hours slower than via Burlington and Brantford, and 2 hours slower than driving. In fact, from the morning Sarnia -> Toronto train, you can do a 50-minute transfer at London to another VIA train that will get you to Toronto 33 minutes earlier along the faster route.
Edit: here's the timetable: https://www.gotransit.com/static_fi...Planning/FullSchedules/FS25062022/TABLE31.pdf
Speaking of pilot projects, a portion of the route (Kitchener) will be GO's first electrified segment.