Thanks for the photo. Mine is similar as you said (I will post upgrade soon), but the X ballscrew is on top of the axis.
I plan to use 1605 screw for the Z axis with a 2.2kw spindle. The distance between X rails and spindle will be ~23cm.
I think, with this configuration, it will have more leverage. Is it right?

I will try to put X rails on top and bottom. Thanks for the advice ;)