I'll echo what others have said and add a small list of test material. It does depend on your source and it's original format. If you feed a pro-scan component input from a pro-scan DVD or HD device, then obviously the iScan will be moot. But when it comes to interlaced material you need to judge the iScan using a variety of video.
1) Film originated (24fps) video will be processed differently by both units. Any major movie on DVD will do.
2) Video originated (60 field) video will also be processed differently. Any sports event or newscast is shot in 60i, and will be a good test.
3) Film or CG originated (30fps) material, which is somewhat rare, are handled differently. As of this time, I know of only one somewhat major DVD shot in 30fps: "Oklahoma!" ..Most CG for film movies, like "A Bug's Life", are rendered at 24fps, as they will end up going to film.
4) Going into ultra-rare material, field-sequential 3-D video will be processed differently, by either making or breaking the 3-D image. The IMAX 3-D DVDs are great demos.
If I were to take a guess, I'd say the X1's internal will probably end up being better with film and 60i video, but note that is still just a guess.