I'm the punter who has probably contributed most to the Oxygen Emate thread linked above. My commute is 9.5 miles over an undulating route and with slow, heavy Schwalbe Ice Spiker tyres fitted I can do that in 33 minutes (with Schwalbe Land Cruiser tyres I can do it in half an hour on a lower power setting). Even on the lowest, Eco, speed mode the bike gets me up hills very well. I should add that I am a reasonably fit cyclist. If I up the power to Normal it is even quicker. I have hardly ever activated the Speed mode, as the bike in its unrestricted form is rather too fast for my tastes in an urban setting in that mode.
I have managed 35-40 miles on the Emate at such rapid speeds. Were I to limit it to 15.5 M.P.H. the range would increase significantly.
The equipment on the Oxygen is very good quality stuff; Lookin saddle, decent Shimano gears - not cheap Tourney ones, and powerful hydraulic disc brakes. Assuming all the above applies to the S-Cross, you'd be buying a very accomplished and versatile bike.
I can't comment on the Momentum, as I've no experience of it. As others have pointed out it's a very different machine. Sort of like comparing a Ford Focus (Momentum) to a Nissan Qashqai (Oxygen).
I have, however, used the SRAM Automatix hub on an ebike I converted. It was surprisingly well suited to the task. The sprockets it uses are the Sturmey Archer standard type, so cheap, meaning that I could easily fit a smaller sprocket than I had on the unpowered machine. That raised the gearing so that the automatic up change happened at c.11 M.P.H. The upper gear was good up to about 20-22 M.P.H. when I would start spinning out. The down change requires you to stop pedalling a fraction of a second, but is seamless. It's fine for a commuter, but would lack the versatility of my 27-speed Emate.