DblXXX modes and Productivity are a pain on ECS - essentially it's the SuperHires output mode combined with increased horizontal scan rate. This means you can only run 2 or 4 colors AND the latter will saturate chipmem bandwidth (just like 16 colors in Hires).
Time to think about a graphics card - but then again it's only Zorro II, so a flicker fixer might be a better choice.
