Bitcoin Mining with Old VXes?

[interfect]

Someone on Reddit had the idea of digging out an old VX and configuring it for Bitcoin mining. The people over there seem to think it may or may not be capable of pulling a few Ghash/s.

Has anyone tried this before? What hash rate might be expected from the different models (old VX 2s and 3s vs. the new VX 7)? Might it be more cost effective to just buy a new 7 and use that?