@jens55 The extra weight of longer belts on a core XY is insignificant as is the weight of the moving idlers when compared to the moving mass of a "bed slinger". Couple that with the fact that both motors contibute to motion for anything other than 45 degree moves and the 1.4 gearing effect on those moves means that a CoreXY will always have more torque available than a Cartesian. The only exception might be 45 degree, single motor, high speed moves where, because of the gearing effect, the motor turns faster and could potentially reach the point where the torque curve starts to drop. But it would need to drop to the point where the torque is 1/sqrt2 of peak torque where it might become an issue. On my machine, with my motors, that's about 550mm/sec.
By way of an additional data point, I used to have 6 extruders mounted on a second (UV) gantry above the XY gantry. The moving mass of this set up was circa 3Kgs which I could accelerate at 2000m/sec^2 up to 350mm/ sec using a pair of Nena 17s with quoted torque of 59Ncm..
