I know that progessive frames like up a lot less storage (for the same quality) than interlaced frames. Each interlaced frame is really two frames in one (fields).

So for the same bit rates, progressive "frames" are much less artifact free then interlaced "fields".

Remember Kakus clips (except one) are also 24fps and not even 30fps, and so there is even more allocated data for each frame.

Personally I think that unless there is a lot of movement, at 24fps there will hardly be any noticable MPEG-2 baddies...

<<If you shoot in CF25 on the Z1U, does it produce less artifacting than in 60i?>>

For sure.