Stay on 4.1, if you come to 5.0.2 say goodbye to Cydia.
I know if you upgrade to 5.0.2 and jailbreak it, you can add XBMC to it.
As for me, I haven't looked into it yet, been to busy. I don't know much about XBMC but I really want Plex back on my ATV2, and I haven't seen anywhere on how to install it.