When I shoot Sony HDCAM for slomo I shoot 59.94i. The post house I use then does their magic, turning fields into frames then outputting back to 23.98psf. So, the material being filmed out is progressive.
I have not been able to see slomo tests on film yet. I did however get to see some of my tests digitally projected on a "big" screen (the Paramount theatre, for those of you who know Austin), I was very impressed.
No noticeable resolution difference from the non slomo HD material.
I have a couple of projects coming up this year (fingers crossed) that will require slomo film out tests. I'll let the list know the results.
Ian Ellis DOP