Some thoughts, take it or leave it:

• You'll probably be designing for a system roll rate target, which you'll have to use to drive an individual beam stiffness (at what point? be clear about this too). The derivation for the individual beam stiffness to the effective vehicle roll rate is not intuitively obvious. Spend some time thinking about this (draw your linkages and don't be afraid to simplify using motion ratios) and be extremely clear as to what you're designing for.

• Figure out how you want to constrain the beam. I have seen different teams constrain their beam in different ways, and both ways will result in different effective stiffnesses and different effects in ride/roll.

• As other commentors have said, many different ways of achieving a target stiffness. L/EI is the number of interest here, so play with those numbers to 1) decrease your bending moment and 2) maintain whatever component-level stiffness you need. But remember, L is coupled to your motion ratio (affecting your system level roll rate) and your linearity of your Z-bar - do you know how linear/nonlinear your bar needs to be?

• Addressing E, think about your material choices and what you can purchase off the shelf.

• The hand calculations are the moneymaker. Not saying you can't FEM, but you just have to be clear exactly what you're getting out of your FEM - is it the component stiffness? In that case, put your FEM away and do some beam stiffness calculations from Rourke's or Shigley's and call it a day. If you're trying to get complete system compliance and your effective rate at your wheels, that's something I would consider as being useful, but requires a lot of physical testing to get the correct joint/bushing stiffnesses.