I see what your saying and I'm probably wrong but 275% of a 350w motor is still more than 300% from a 250w motor. Again I'm probably wrong but power = watts not torque. Sorry so many question
The Newton metre figures quoted on the website indicate the motor labelled as 350w produces a bit less torque than the CX one.
It's all moot anyway, given how hard it is to make comparable torque measurements.
As regard power, 275% or 300% assist doesn't mean a lot, which is why I called it Bosch speak.
As I said, I doubt you will be able to tell the difference between the two bikes, even if you rattle along in turbo all the time which few users do.
You either want the 28mph assist one - which will be harder to find and more money - or you want the 15.5mph assist one.
Of all the figures you are rapidly bogging yourself down in, those two - 15.5 or 28 - are the only two that matter.