Mac Pro or PowerMac G5 - Via Mac of all trades

I've bought and sold Macs to them over the last 3 years and they are a very reasonable company to work with. I personally bought a Macbook Pro from them for school work and the machine arrived in excellent condition, and with original manuals and disks, despite the warning that it would not include those things. I think they've been in business for well over a decade too, so they must be doing something right.

The prices for the units you've listed seem very fair, and as long as you're ok with the fact that neither of these units will run beyond 10.7(10.5 for the G5), it ought to be worthwhile.

 

MacofallTrades on the up and up

I would have to agree here. I have bought at last count 4 machines over the last 6 years from them, and all where as promised in great shape, packed really well and shipped on time.
The only issue I ran into was with my PB from my sig I purchased from them. It came with a crappy keyboard with a ton of loose keys and 10.4.11 installed when the advert plainly said 10.5. A single email and phone call later, replacement keyboard and install for 10.5 was on the way. No issues after that. In fact, I am looking to buy from them again to replace the PB, with a newerish macbook pro.

 

MacOfAllTrades is fine. We've purchased some older, off-lease MacBook Pros from them. One could find better prices on eBay with a little patience, but if you want the convenience of dealing with an actual business, then they're worth buying from.

Also consider MegaMacs. I comparison shop between them and MOAT and purchase from both. MegaMacs seems to have slightly better deals on Early 2009 Mac Pros at the moment.

If you can spring for the $899 for one of the 2009 Mac Pros instead of a PowerMac G5 or a 2006 Mac Pro, you will be much better off in the long run, as the newer models will run Mountain Lion, take much less expensive RAM upgrades, have more options for video cards, can be firmware flashed and the CPU can be upgraded.