I have a feeling I have turned the composite circuit into somthing with good AC impedance, or horizontal plate lines. Even better than the traditional triode-on-a-triode cascode.

The upper element of the cascode does do one important thing, it determines where the horizontal, pentode-ish plate characteristics start, relative to the Ec2 voltage. I suspect that the pentode offers a lower voltage start, and more horizontal when they happen, set of plate characteristics.

And I have a day job which gets in the way of serious experimentation.
regards,
Douglas