Wow, didn't expect to see this thread still going. I've tried XFCE on my desktop, and it just never seems 'finished' to me. I think I'm biased towards Cinnamon because I use Linux Mint on my desktop and I never really liked Mate since it was like going back in time.
I have a pretty anemic system as the system I use the most, a fitpc3 (got it before the mint edition came out sadly) and Cinnamon runs fine. I know there is a huge power difference between ARM and x86 though.
I remember before the Pandora was finished I was asking about KDE 4 and that wasn't even done yet. I don't like XFCE on my Pandora though, I think I could survive it if the screen resolution was higher, like the Pyra will be, but when I plug it into a monitor(HDMI out, yay!) and have a mouse/keyboard plugged in I'll want something more substantial. If the Pyra isn't powerful enough I will use XFCE though, I don't hate it by any means.