i wouldnt try 2 jar's thats for sure...i've seen 2 large Black aro's co-exist in a relatively small tank for that matter

(LFS) keepin an eye on them for about a month now...seen no visible scars, no fins torn, no bumps...they actually swim side by side the whole time! its an awesome sight..
but, all in all i agree with the above posts..."you never know until you try, each fish is different."
-ROB