Start with a 25p sequence, drop some 50i footage in there with the 25p footage, export a couple minutes to create a test DVD or bluray.
Then make a new sequence 50i, put some 50i footage in there and then add some 25p footage in there, export a couple minutes for a test.
Chances are one of them is going to look just fine for you.
I too, on occasion, have to mix i and p and it works out fine.
Only Deinterlace when compressing final master for web delivery or computer presentation.
Chris Tompkins
Video Atlanta LLC