Well, there's good news and bad news on the Cube project...
The good news is the PowerLogix 1.7GHz PPC7448 w/ Cube VRM bypass arrived from OWC right on time, was successfully installed, and appears to be working perfectly (posting from the Cube presently). The machine is actually really fast now - boots in less than 30 seconds (haven't timed it yet), opens apps in just a bounce or two, and is quite Teh Snappy.
The bad news is that I think I damaged the GeForce 6200 that I had been using; the machine wont boot with the card installed. Boots fine with the original Rage 128, but no go with the GF 6200. I think I might have rocked the heat sink when removing the card, which could have damaged the chip underneath. I'll try it in my Gigabit Ethernet G4 tower later on, but at least that's the easier/cheaper part to replace. As long as its not the processor, VRM or the motherboard, I'm happy.
I can't check temps as the processor either doesn't have a temp diode or it isn't supported on some combination of hardware/software, but I do not feel any unusually warm air coming out of the top of the machine - for what that's worth (yes, there's a fan).
Here's a couple of pics...
I'll have to decide what to do about the video card. Presuming the card doesn't work in the G4 tower, then I'll look at replacing it, ideally with something a bit more, uh, robust. If it
does work in the other computer, well, then I've got some major troubleshooting to do on the Cube. Not sure why it wouldn't boot since everything else appears to be running just fine, so likely the card is dead.
As quick as the machine seems now, it should feel even faster when I get a proper video card back in there. With the Rage 128, the CPU is having to do all the rendering (like the Dock scrub effect, etc). The Dock effects were unbearably slow on this video card with the original 450MHz processor, but was very responsive with the GF 6200 plus the original processor. With the new processor, the effect is essentially the same as it was with the better card and slower processor (though its still stealing processor cycles from whatever else is going on). It should be really great with a proper video card.
I'll continue to post updates... But for now, the Cube is running remarkably fast for an 8 year old Mac.