Deutsche Bahn doesn't manufacture rolling stock. They buy it from Siemens, Stadler, Talgo, Alstom etc...
Edit: AFAIK, some of it - mainly high-speed trains - is designed according to DB specs and subsequently offered under a new name (and with changes) to other train companies. For example DB ICE 3 (manufactured by Siemens) / Siemens Velaro.
It does happen occasionally, but DB tends to run, maintain and sometimes upgrade its successful (~reliable and widely introduced) rolling stock until it falls apart or is grossly outdated (40+ years old). Rail passenger numbers are increasing, so there is no need to sell stuff to downsize.
The Flixtrain company uses 40+ years old IC (intercity) cars - they have no air conditioning and it's really loud inside with open windows, especially so in tunnels. That is the kind of stuff that DB sells.
Hrrm. Funny. I thought that those were so called "Eurofima", which I remember as fucking cold in summer, because then their AC were set at full blast, which was annoying at the times.
Incorrect. They wouldn't fit in the tiny UK loading gauge (profile). UK trains are indeed variants of continental models, but made to custom size, and many (most?) of them in the UK.
Everything about UK rail is custom (apart from the gauge). Apparently it's one of the (many) reasons HS2 is such a mess.
They were trying to run trains faster than typical continental high speed lines, which meant custom design work that needs loads of additional testing and certification. Rather than just use the Spanish or French high speed designs.
Max line speed of HS2 is 360km/h, with provision for 400 in some sections in future. This is entirely in line with many other modern HS lines. China’s been running regular 360km/h services for years.
This is a project with a 200+ year shelf life. Designing to 300 or less would have been short sighted, and many of the changes to accommodate such high speeds actually reduce costs in the long term (slab track, headroom to catch up delayed services, ability for one trainset to operate more services per day etc).
The cost overruns of HS2 are primarily from plain old poor project management, complex planning law and constant political meddling, not engineering decisions.
China has run at 360kmh before, but last I checked they mostly run slower.
Air resistance is a killer as you go faster. So for trains 300 is usually about the best compromise between energy use and speed. If you want to go faster a jet at altitude is going to be much faster at a better fuel efficiency. High speeds make sense for long distances.
Edit: AFAIK, some of it - mainly high-speed trains - is designed according to DB specs and subsequently offered under a new name (and with changes) to other train companies. For example DB ICE 3 (manufactured by Siemens) / Siemens Velaro.