The 2.7 GHz was not an early liquid cooled system - it was one of the last.
PowerPC systems still make plenty of sense depending on what you're doing. A G4 is easily on par with an Atom system, and a G5 can still do respectable amounts of work. In FInal Cut, for instance, a dual 2 GHz G5 can edit 2K ProRes quite reasonably, as an example.
I just set my wife up with a 1.66 GHz PowerPC G4 Mac mini so that I can fix her 1.83 GHz Core 2 Duo system which is a little flaky, and she hasn't had any issues with perceived speed. Considering how much she's on YouTube, that's pretty good.
If I had the need, I'd be more than happy with a price of $250 for a dual 2 GHz G5 or faster. It's an excellent price.