I did use a zoom along with the Primos. Panavisions terrible little rehoused Canon lightweight zoom. I think it is 28-64mm, t 2.6. The good thing was that I didn't need to use Classic Soft filters on it to match the Primos with the filters! I was hoping to get their new LWZ, but it wasn't available.
I am an ARRI guy. I love the choices available- Angenieux Optimo zooms, Arri Master Primes, Cooke S4's, etc. AND, I love the Arri cameras. As an operator and DP. I will try the D20 next Digital job because of the optical viewfinder. And if the slow relative ASA rating is true, it might be closer to what I got on the Genesis when I really needed the speed!