First time working with HDV 1080i50 - confused!

I'm editing HDV 1080i50 for the first time. The finished film is going to be encoded for the web in H.264 at 720p25, so some de-interlacing needs to be done. Usually I edit progressive DV-PAL, so I'm not used to de-interlacing. I've been playing around with the Nattress Film Effects plugins demo, but none of their de-interlace options give a satisfactory look. Standard de-interlace (e.g. discarding half the fields) looks a bit lacking in detail, and a 'smart blend' de-interlace just blurs the fields together (no, the camera guy did not get the shutter speed correct) so all of the handheld camera movement becomes a blurred mess.

However, I discovered (at random) that if I go into the sequence settings and set the field order to 'None' it has the same effect as discarding the upper fields, but actually leaves things looking sharper than with using a dedicated de-interlace filter. Any lack of smoothness to edges will surely disappear when it gets downscaled to 1280x720. So I guess my question is... what is going on when you turn off the field order using HDV 1080i50? Is it simply discarding half the fields? Also, if I'm going to be using this de-interlace method (and I don't see why not) is there any advantage in using HDV 1080p25 instead of HDV 1080i50? And finally, could it be wiser to use ProRes 1080p25? I've got a lot of titles and graphics, and though the HDV codec seems to do an OK job of rendering them, I'd like to know if ProRes will be better/faster. =)