I've seen lots of people keeping arros in 2' wide 6 foot tanks, I'm sure they would much rather appreciate a whole foot of width as apposed to length.
I am planning to an Arow tank at some point and this is what o understood to be the minimum as well. The 6 footers don't provide room for the fish to turn. While being only 5 long is not ideal at least it can move around. Also for the record Clown Loaches can get about a foot long so 50 is out of the question but they are super cool fish! Geos are awesome too. You have the length for a big Poly so that could be a good choice.
excuse the typos sent from my Droid Inc2