If you shoot at 30p then import that footage into a 23.98 timeline and set it’s speed to 80% you can get frame for frame full resolution slow motion from the DVX100. It looks really smooth, but it’s not as slow as you want some of the times, cause your really only locked into that one speed to be able to keep the resolution.
As for converting 60i to 23.98 with software or just shooting 24p Advanced, you’ll save yourself the headache of waiting for the software to process it if you just shoot 24p Advanced to start, and the software I’ve seen doesn’t look as natural as the in camera, because the DVX100 literally shoots at 23.98 fps in that mode and it’s just encoded into 29.97 to fit the DV codec. If you remove the extra frames on import you get the exact same 23.98 fps that you shot and not some interpolation of what it could have looked like.