Why not add a 3rd 846 Or an 847 for that matter?Well...I just picked up two Chenbro 48 bay top loaders (getting my 846s out of the rack) with an X9SRL-F motherboard for $400/ea shipped. That motherboard itself is probably ~$100-$150. So, the chassis really was $300ish shipped. And that has a proper SAS backplane (6gb/s), no eSATA stuff. That said, it'll require some surgery to put in alternate power supply(its), as the stock Zippy ones are trash.
Comparing the Chenbro to this, I'd pick the Chenbro every time.