I still have more playing around to do, since there are a lot of settings and I have a lot of different situations to test out when filming. So far, I'm impressed by just how much better the XA20 is over the XA10 for me and for what I use it for.
The big difference right away is the quality of filming at 1080p at 60fps. I can see the difference between filming at 60i vs. 60p without any effort. Even when I did some test recording on a Blackmagic drive to see if it would be worth picking one up or not, I noticed right away the difference between the quality of 60p recorded in camera and the "30p" recorded on the Blackmagic drive. The drive converted 60i to 30p and the loss in image sharpness was amazing. (The drive doesn't support 60p input through HDMI.).
Though I did notice less compression artifacts in the ProRes (HQ) codec recorded on the BM drive, the pixels were all larger than when reordered on the camera. Recording in 24p, which BM says should work isn't an option for me because I hate that look. As far as any compression artifact problems in the on board recording, it was really only noticeable when I really tried to trash my footage with an insane amount of brightness and contrast adjustments. Even then it was only reserved to the darkest spots of the recording (blacks). If the colors weren't that dark then I couldn't find any artifacting even when the video was adjusted to extremes to look for problems.
As far as any extra gains 4:2:2 might add to color correction, I couldn't find any. The 4:2:0 footage held up just as well under some pretty extreme grading. If anything the ProRes footage looked worse because of the larger pixels. Surprisingly even color keying worked better with the MP4 footage compared to the ProRes. The higher resolution gave sharper edges and a better all around key for almost all the colors I tried. Only yellow seemed to be slightly better under ProRes.
All that means for me is SSD 4:2:2 recording through HDMI in a Blackmagic drive isn't something I'll be looking into. The loss in picture resolution and no obvious gains anywhere else just don't make it a worthwhile addition. Some quick looking around on BM's forums show other people have the same problem with getting proper progressive recordings on their gear and they've said that 59.94p recording isn't on their list of priorities even though the hardware should be able to handle it and it's a much requested feature. Sometimes decisions like these just leave me scratching my head. So in the end, the compression artifacts that AVCHD and MP4 have in the very dark colors is something I'm more than happy to live with. I can't think of anything I'd shoot that I'd need to brighten up to the point where it becomes visible or a problem.
I finally had a chance to seriously play with the new image stabilization system in the XA20 for a continuous shoot of about 40 minutes and it was amazing. I'm seriously blown away by the quality of it. Canon did a great job with it and I was able to do things handheld that I've never been able to do before. Tying into that, the 20x zoom is great and a huge step forward from the XA10. I was able to get some shots I would've never been able to get from my XA10.
What I'm looking forward to now is an opportunity to go out into the woods somewhere and do my thing and really give the camera a go doing what I bought it for.