Ffrom the apple store you can get:

One 2.66GHz Quad-Core Intel Xeon

3GB (3x1GB)

640GB 7200-rpm Serial ATA 3Gb/s

NVIDIA GeForce GT 120 512MB

One 18x SuperDrive

Apple Mighty Mouse

Apple Keyboard with Numeric Keypad

for 1899£

these are price for a NEW machine not a obsolete G5's and even if they look pretty much similar, they have BIG differences in the case structure/design, engineering of motherboards and so on.
Not just in the speed / performance of the machine itself (or the name).
They also emit so much heat from the fans, while they are doing the same amount of work a new macbook pro can do easily.

I'm not trying to be bitter or something, but selling your 1.1 g5 POWERPC ( is not even INTEL processor so not good for new software or to run windows) for 1200/2000 £ sounds to me a bit pricy.
Even if they have 2 or 4 processors (not compatible with all the software anyway) are still slower than 1 2.66GHz Quad-Core Xeon
Same for the ram, no even after effects is compatible with 8Gb of ram, so pretty much useless to have it, if not using a compatible and specific software.

Just my opinion, of course and again i'm not intending to offend anyone, but I wanna advice someone that might be interested and not too much into Mac as I am (but looking at the case might think: oh is like the new ones !)

I think that personally i would suggest whoever will buy them not to spend more than 600£ collected. But again I would buy a G5 only for a very specific use, as those are very pro machines and not versitle at all (heavy, noisy, heat emitting etc.) and even if obsolete atill good to do some job (running music software etc, video editing etc, but not in my lounge or bedroom)

Just a thought to be helpful to the ppl on the forum, again, not trying to offend Skoota here.