The ROM we have for the 7800 GTX is already for the 512MB version, so fortunately that is covered. The problem is actually the opposite: we lack a 7800 GTX ROM for the 256MB version. I have no idea what would happen if the 512 ROM was flashed on a 256MB card... At best it would work until it tries to access more VRAM than the physical limit, and at worst nothing of it will work.
As for editing the ROM to be able to detect more VRAM for the X1950XTX, reading about it everywhere online gave me the impression it's not feasible. But you know, I wonder about that myself everyday. (Same goes for a 256MB 7800GTX ROM).
For the GTX, I wonder if using the unmodified 7800 GT (not GTX) ROM would do the trick? Both have 256MB of VRAM.
About the X1950XTX, I
do have one idea, but I'm not sure what the odds of success of such an approach are. Both the X1950XT and X1950XTX have a fully-functional
PC ROM/BIOS. If we do a comparison between the two binaries, and see where they are equal and where they are different (I think a number of tools can do that), it may give us an idea where to hex-edit in the corresponding Mac ROM/BIOS that already works for the X1950XT. Although this assumes both the XT and XTX have the same ROM sizes. I didn't check (yet). If different, this may be a lot harder.
In any way, as with lots of things, it's possible. "Where there is a will there is a way."
Although the true way to move forward with the G5 is to go get modern PCIe 3.0 cards working, even if partially (due to PCIe 1.0 speed limitations). But for me, that can wait until I'm done with the XTX.
(I'll be able to get my hands on a strong-enough power supply to do the flashing with within a week. In both times, I had to borrow it.)
Incidentally, I do have to say one thing: I don't yet know what to do with "so much power". As in, I tried finding the HEAVIEST programs in graphical tasks I could find for the G5, and for starters I decided to give Doom 3 and Quake 4 a try at the most maximum of settings (on my non-HD, puny single-link DVI monitor, though). Everything plays smoothly "too easily". By that, what I mean to say is that I'm struggling to find software with which I could really push the X1950XT to its limits. Maybe I'd be able to tell the difference in higher resolutions, but the official GeForce Quadro, although weaker, is still strong enough to also play these games
completely smoothly.
By that, I mean to say, for all other PCIe G5 owners out there, the official Quadro can easily be considered a "good-enough goal". To give words of encouragement to anyone who, for whatever reason, doesn't have one of those flashed GPUs.
