So those charts were made with a 250A controller?
No, they're just the ratings at for 10minute continuous use at 35deg ambient with 8 l/min water cooling. This is the limit of the motor to withstand that power for 10mins - which is a long time by the way, and 70kW for 600seconds is nothing to scoff at.
The document later states "The cooling system was found to be quite
powerful: the limiting temperature of the inverter was never achieved, a reduction of power output was always due to the machine winding temperature." - And it's a 400A controller, so that should put your concerns at ease.
A peak of 70kw isn't gonna give it much of a leg up on the HPEVS systems.
A higher peak is given on the Siemens data nameplate as 3min rating, or 0.5min rating in the graph you linked.
The HPEVS is probably rated peak for <1min for marketing purposes (though i know nothing about the motor and haven't checked), you've got to compare apples with apples - and probably what's the most relevant is the continuous ratings. Some manufacturers rate at 60min, if so, the graph I provided shows about 55kW cont @ 35degC ambient.
If Siemens says the maximum current is 280A RMS (~400A peak) for <3mins, I'm inclined to believe them. You can push it harder say for 10seconds with diminishing returns if your only increasing current (hitting saturation), but it may take 10seconds to hit 150deg from 35deg, but 5minutes to cool back down to 35deg to do it again. Also if your increases the temp so quickly, you need very fast response of sensors and controller to turn it off in time without doing permanent damage to the motor.
It sounds like you are after a more powerful motor, then buy the 5138 or a PM motor.