Plan 1. You can get about 120 mph if you ride it off Beachy Head. Range will be 535 ft unless it's a particularly high tide.
Plan 2. Ride your bike 20 miles a day. Every week, increase it by 5 miles to 25 miles a night, 30 miles, etc. You can stop increasing when you get to around 50 miles a night after about 6 weeks. Carry on for another 10 weeks. After that, you'll be able to pedal bloody fast.
Plan 3. Get a dongle. Be aware that Bosch are playing tricks with their firmware to give hassle to dongle users, so take advice from Ebiketuning before and after you purchase that bike to make sure you won't come unstuck.
E-Bike Tuning
www.ebiketuning.com
Plan 4. Buy a different bike that you can derestrict yourself, or convert any bike to electric with parts that give you the speed and power you want. I can't see the point in planning to buy a bike that doesn't meet your requirements. You can buy perfectly good derestrictable or unrestricted electric bikes on Ebay for half the price of that Cube. Hub-motored bikes have lower running costs and are more reliable than what you suggested, so are better for commuting anyway.
You don't have to spend a lot of money to get a better bike. Ask yourself what "better" means. Is it more comfortable, more reliable, faster, more powerful, more user-friendly or what? Ask those questions about that Cube compared with alternatives.