The big difference between PCI-E and previous interfaces is the fact that it can simultaneously send data both up and down the interface at a consistent rate. There are also of course little differences is larger overall bandwidth and more efficent power design
As for this, I have to say that the marketing department for nvidia is making some pretty silly choices right now. On one hand, they have a 6800GS that performs on the same level as the 6800GT, whereas they have another 6800GS that performs considerably worse. And then they introduce a 7800GS that performs the same as the former 6800GS roughly...seems it would be much easier to simply have called it a 6800GS and scrap the original 6800GS for AGP or call it a 6700GS or some crap...and then they have multiple 7800GTX cards, some of which are nonexistant
Games will get to the point where they will be bottlenecked not only by the AGP cards, but by the processors that are paired with those older motherboards as well.
Now this is just plain silly, I fail to see how a motherboard has any bearing whatsoever on framerate unless we're talking about an issue similar to nforce3 chipsets and nvidia GPUs...although no evidence points to anything of the sort and the stuttering issue with the nf3 has long been a known issue with older games and will no doubt have the same issues with newer games
Without "EYECANDY" PC games are useless.
You can't play a FPS effectively on a console unless they were to completely redesign the controls. Once again there is far too much emphasis put on eye candy and most people seem to forget the point of games is to play them and be challenged, not worry about framerates or anything of the sort
If you intend to buy a video card and are disappointed that it doesn't pull its weight a few generations later, you need to quit PC gaming and possibly find some different hobbies