[Geof]

I would expect them to be the same because they have the same Z travel and I think most of the flex in a vmc comes from the head assembly.

Unless the part being machined is really tall the distance from the X and Y ways up to where the tool is cutting will always be shorter than the distance from the Z ways out to the spindle centerline.

EDIT;

I read what I wrote and realised I am twisted around; the distance from the Z ways to the spindle centerline has to be increased for a longer Y travel so the 3 could be more flexible.