Deciding on processor upgrade for Sawtooth

So it's getting to be time to upgrade my old Sawtooth. Right now it's a 550mhz (overclocked 450), with 1gb ram, ATA133 PCI card, USB2 PCI, and an LG multiformat DVD burner. I plan to keep this thing in some form or other for awhile, and eventually putting in bigger hard drives and 2gb ram, but first comes the issue of the slow processor. Doing Photoshop and Illustrator work with 550mhz pretty righteously sucks.

But I'm having trouble deciding exactly what upgrade route to take. This is one of the older revision boards which will only suport a single processor, which complicates things a bit more, too.

Here's what I'm looking at:
Powerlogix 1.2ghz for $179
933mhz Quicksilver board on eBay for ~$100, overclocked to 1ghz, or,
newer logic board and dual processor setup, prolly ~$180-200.

I see advantages to each route, and I'm looking to keep the upgrade under $200 simply because it's a 6-year-old computer, so I'm really looking for the best cost-benefit. Would a Powerlogix 1.2ghz upgrade really be much faster than a 1ghz Quicksilver processor? I know the Powerlogix has twice the L3 cache, but the QS proc has twice the L2 cache... Even if the Powerlogix is faster, is it $79 worth of faster? The install difficulty isn't an issue here... I'm an electronics nerd and like doing that sort of thing.

Then I have the dilemma of going the SP route, or just replacing my logic board and getting a DP setup. I wouldn't need nearly as fast processors if I had two of them, so I could conceivably go even for a cheap set of dual 533s and overclock 'em to 650mhz. Then I'd also have the option to upgrade again later if I wanted to keep this as a second computer. But, logic boards are pretty expensive still, so I'd probably have to stick with another Sawtooth or Gigabit Ethernet board to keep the cost down, leaving me with the 100mhz bus, 2x AGP and such.

So, any recommendations? I'm not looking or a supercomputer here, just something that'll last me a couple more years. I've also considered just putting it off until I can afford a new Mac, but I want to stick with PPC until Adobe gets their s**t together on a working Intel build of CS2, and there's no sense in getting a G5 when I could just spend another $200 to have my G4 suffice for another couple years.

Maybe I didn't emphasize these points clearly in the original post, but:

Selling the whole computer is *not* an option at this point, considering the other upgrades I have in it and some cooling/cosmetic mods to the case. The best I could do on that is maybe find a DA logic board to swap into the case.

$300 for a DP upgrade is *not* an option, since my budget goes up to about $200, maybe with a little leeway, but I see no point in putting much more into such an old computer.

I don't care about the extra work to install a QS processor, I already know how to do the ATA connector thing and the 12V mod... take me about 20 minutes max to do.

And I've already checked, the computer has the Revision 3 ASIC and will not support dual processors in its current form.

So, back to my original question... all other things aside, is the Powerlogix chip that much faster than a QS processor overclocked to 1ghz, that it would justify nearly twice the price?

And if I went for the logic board swap and an OEM DP set, what sort of speeds would I need to give me an edge over a 1-1.2ghz SP? Running some 533's at 650 or so would be my low-end I think, and I'd try to find the fastest ones I could within budget.

And, not intending to sound like an ****** here, but unless there's some amazing cure-all option that I haven't thought of yet, I have already weighed my cost-benefits through a great deal of research and narrowed it down to the three options I stated, and I only want real-world advice on what would be the best of the three, considering both speed and cost.