The 2.7s as a whole are more reliable than the 2.5s. These are also the fastest PowerPC computers made in terms of single-thread performance.
I love my dual 2.7. It's not as fast as my Quad, but for a lot of the stuff I do it's faster.
I'd go for it. If you do buy it, check carefully for signs of leaking. The stock LCS uses a dyed liquid with noticeable UV fluroescence(fluorescene).
Under daylight, it's pale yellow-green. If you can, try to examine the case bottom under UV/black light and look. If the seller will let you, pull the "G5" cover off the processors and examine the LCS carefully. Pay particular attention to the black mat material(pig mat) under the LCS. Also look for corrosion on the bottom plate.
Many folks will call these a ticking time bomb, but I'm of the opinion that the problematic ones have likely already been filtered out and any left in working condition will likely work for a while longer.
If all checks out with the LCS, I'd buy it. In particular, if you are trying to run legacy peripherals(which I am) these computers are in many ways king. The expansion slots are PCI-X, and thus can be fitted with standard PCI cards. Running 10.4(Tiger) it is possible to run EVERY piece of Macintosh software written from 1984 to 2006 or so(and of course universal binaries made after that).