That's just awesome! Who cares only 1 PCI-e slot? You can put a GTX 590 in there someday! Just kidding. I think it's an awesome little SIMAP cruncher or PRIMA or RNA or whatever - there are lots of good CPU only projects still, and this one rig will smoke your two old ones put together - hands down, and probably pay for itself (over about 2 years) in utility cost savings.
In all seriousness, a great upgrade. Hope you get lots of enjoyment out of the new rig!