I did not notice any reduction in stiffness going from an aluminum Santana Sovereign to the Calfee.
If anything the Calfee feels better when we are standing on climbs.
Our team weight is 250lbs and we don't put out a lot of power.
We did loose about 6 lbs in weight going to the Calfee but a good part of that was in the components.
What I notice much more than the weight loss is a much smoother ride which is not only more comfortable but allows higher speeds on rough roads.
As others have noted I am sure Calfee can make the frame as stiff as it needs to be for your liking but it may cost a bit more than a standard build.