Upgrading G3 and G4's video cards...
I've begun looking into video cards for both my sister's B&W G3 and my Dad's G4. My goal isn't really getting them able to play games but more able to run Quartz Extreme, and maybe Core Image on the G4. I've found that just having Quart Extreme makes a world of difference. Not only does it make the UI smoother and sometimes more responsive, but it also lowers UI overhead as the GPU is handling a good portion of the work. You've probably already heard about this when QE came out with 10.2 a couple years back. So, I'll continue.
I've mainly been focusing on the Geforce 5200 for the G3, as it seems to be a good card that has a high chance of flashing success. I'm pretty sure you can get Core Image working on it over the PCI bus (for the PCI version, duh), although I haven't heard good things about this. As for the G4, I'll probably go for a 5200 as well. I would have tried to get a Radeon 9800, as they flash very easily from what I've heard, for the G4 and give it some gaming power. I've pretty much already got my hands on a AGP GeForce 5200, though.
I haven't yet gotten my hands on the AGP, for the G4, or the PCI, for the G3, versions of the 5200 yet, but I hope to soon. I'll have to post on my success, or failue, in the flashing procedure for both of the cards. I hope for the best.

Well, as long as you say you're able to securely back up the original ROM, I don't see the downside! Hell, we might even all chip in to get a 9800 PRO just to see what happens. We could get a good open box one for about 55 bucks or so on NewEgg.