Mmmm...Clear understatements. AGP isn't that slow. Most cards even today can't use the full bandwidth of it. You lose 3% in performance when running the first few PCIe 2.0 cards @ 1.1 spec 16x. You may lose another few percent by running PCIe 2.0 cards @ 1.1 spec 8x. At that speed, the bus is running at the old AGP 8x speeds. They aren't fast; its just the cards that run off them cost a hell load of money. Does it justify the costs? If you really want to revive an old PC, you can easily go off and find one of those old 6200s or 7300s with the good old 128 bus and flash them. There you get a 6600 (Vanilla) or 7600GS, etc. Nowadays, they should all cost the same, and you get probably get a cheap card that gets the work done for a mesely 20-30 dollars; if you find the deal. Many people sell old PCs; ask if you can take, for example, the GPU of the PC.
To tell you the truth, many systems can run many games. It is to what detail you want to run them in. You can always run CS:S at blundering CS 1.6 looks, and get that done on the Pentium 3 @ 1 GHz, and some cheap Geforce 2 card. On any case, a rig that was made this year or so would have trouble maintaining a well over 70 fps in Crysis. However, a rig that was built around the Source dominant era could run it at low resolution and detail at ~40 frames.
@Shaun; ehhh, can't you just BIOS flash the cards. To my knowledge [even though i grew up in the later series], the GTO lacked core speed and PRO had 4 pipes locked up. Even then, it doesn't make a difference as they lag behind so much towards current kings that that difference is small; even unnoticeable.
