You won't get any flack for asking about "outdated PPC Macs" on this forum.
With that said, can you be more specific about what programs you want to run?
Depending on what they are, your money might be better directed into either a first generation Mac Pro(1,1) or an older G4 tower.
G5s are wonderful computers, and I still use my G5 Quad regularly. I've also been(slowly) preparing a dual 2.7 to replace a lot of tasks that a G4 is currently doing(although it's been slow because I need to find the correct cards to maintain peripheral compatibility, and those cards are easier to find for a G4 than a G5).
If you're running programs that are universal binaries or(most) OS X native programs, they will likely run faster on the Mac Pro. With that said, you must use OS X 10.6.8(Snow Leopard) or earlier to run PPC native programs. Programs like Photoshop CS2 will run faster on a high-spec G5 than on a Mac Pro 1,1, but it's one of the few exceptions.
On the other hand, if the programs you want to run are OS 9 native, I'd strongly encourage you to find a computer that can natively boot OS 9. Up through OS X 10.4.11, it is possible to run OS 9 native programs through the "Classic" virtual machine, but I've generally found this to be unsatisfactory. Most G4 towers(the exception being the last generation Mirrored Drive Door with FW800) will natively boot OS 9.
Just a couple of other thoughts-
First, most games, especially those that will run on a G5, aren't multi-threaded so won't really benefit much from dual processors. This can save you a lot of money as most single processor G5s are virtual give-aways. With that said, you have a LOT of GPU options for AGP G5s and depending on the game you are running I'd get the best that you can afford.
Web browsing still works well on higher spec G5s, but it's becoming a never ending battle to keep it that way with an increasingly bloated internet. The most popular browser is TenFourFox, which is a fork of Firefox(Mozilla) maintained by a single dedicated individual. It's secure and generally gives accurate page renderings, but can be slow(a good G5 will make up a lot for this). If you are running Leopard(potential program incompatibility if you are running OS 9 native programs) there is also Leopard Webkit, which is generally fast. In both cases, you can forget Flash content, Silverlight(Netflix) and a decent amount of other plug-ins. There are some ways to spoof the Flash version number, but this is a bad idea as you are still running a badly outdated version of Flash with security holes. There are some tricks to get certain content to play through Quicktime, and this can get around the issue. Youtube is comfortable on higher spec G5. If, in particular, you want to watch Netflix an Intel Mac is essentially your only option.
I'm sorry for the rambling answer. I don't mean to completely discourage you from getting a G5. As I'm sitting here at work, I'm typing on a Macbook Pro, have Mac Pro 1,1 to my left, a G5 Quad(that's used regularly) on my far right, and an upgraded to the gills PowerMacintosh G3(with a G4 processor) all turned on in my office in addition to several other PowerPC Macs that get used for various purposes.
@128keaton has seen my office and can attest to this. He hasn't seen my home, where I have the bottom of closets lined with G4 towers along with stacks of them in corners.
