I'm no G5 expert, though there are two of them here, but as I recall from Macworld benchmarks the 2.7 was faster at cpu type tasks than the 2.3 DC (and quad?). However, with the slower Ram it's probably not up to the newer models for other tasks. Not to mention the more reliable LCS on the Quad. If it was me, I would hold out for the Quad, which you can probably get for less than $200 if you're patient.

In fact there was a Quad for $150 on the local CL a few weeks ago.