Jim's right, if you are no longer running bias plys the stock alignment is not applicable (although many unknowingly still use it). As a matter of fact, it's quite the opposite.
I wouldn't worry about the caster affecting stiffness unless you are running non-powersteering. As Jim said, shoot for as much caster as can be dialed in with stock arms, aim for about 1/2° negative (stock is positive)and about 1/16 to 1/8" toe-in.
