Here is the calculator I wrote some time ago if you want to compare sections
http://www.mycncuk.com/threads/2214-...ess-calculator

Of the designs you have drawn they all have the ballscrew next to the YZ axis which is compromising the gantry stiffness.

A popular design here is the L shaped gantry with ballscrew tucked behind. Away from pc so will post example later or someone might post it.
L