I am shooting video for a customer, who requires the footage in PAL DV (576i) format. As my 60D only records progressive video, I use Fieldskit Reinterlacer in post to make the footage interlaced. I opt to shoot with 50 frames/sec (720p50) to make motion a bit more smoother after reinterlacing. Motion never looks very smooth with 60D and I am ok with it, as I try to avoid quick panning etc. while filming. However, I am not sure which shutter speed to use, 1/50 or 1/100. 1/100 would be the normal choice for 50fps footage, but now that I am reinterlacing the 50p footage to 25i in post, shouldn't I stick with 1/50, which is usual when shooting 25fps?

I think you are fine with 1/50 even when shoot 50P if you want it to match 25i

Fieldskit is supposed to smooth the sometimes apparent stuttery motion of p footage with fast action, if you don't have too much movement you don't need Fieldskit, and I can't see any benefit from it whatsoever if you're shooting 50fps since your editor is putting each frame into a field. For shutter speed, 1/50th has become standard for 25fps, if you're shooting 50 fps to go to 50i, shoot at 1/100th to match 50i at 1/50th.

Thanks a lot for your replies!