What is the differnce of AGP 3.0( 8X ) and AGP2.0( 4X )

Question

I test some Nvidia graphic cards  that support AGP 8X and test them in 3d mark 2001 (with AGP 8x and 4x) and I have not seen any difference on this 3d mark version.
I know that AGP 8x is  2.1 GB/s    and AGP 4x is 1.05 GB/s  but the differece of them must be shown at the games tests.
Is it the END OF AGP GRAPHIC CARD ?
Is it true that from 2005 intel and hp want to use PCI EXPRESS in their PC or notebook?
If it is true
why we pay more money to buy a new 8x graphic card(without any improve in performance from AGP 4x)

Answer 1

lionking1467,
From Anand Tech:
Quote
In theory, a faster AGP bus with more bandwidth means that more vertex data can get to the GPU and thus speed up the rendering process. In reality however, we aren't coming close to saturating the AGP bus and AGP 8X barely offers a performance improvement over AGP 4X.
NVIDIA Introduces GeForce FX (NV30)
From Tom's Hardware:
Quote
Now we´re sure there are some readers out there mournfully looking at their now "outdated" AGP 4x system. But is the twofold increase in speed really necessary, not to mention - tangible? To be blunt: no. Even future applications are unlikely to require a bus interface that is faster than AGP 4x. 8x is more of a future investment than a current requirement.
While AGP 4x with its 266MHz offers a maximum theoretical bandwidth of about 1.1 GB/s, 8x allows for twice as much data to be pushed across the bus, namely 2.1GB/s. Additionally, there are now several new side-band addressing modes as well as an "isochronous operation" mode, which ensures maximum available bandwidth regardless of system load. This could prove a very valuable addition for video streaming and similar applications. Games, however, aren't nearly as demanding, making this a moot point for gamers.
NV18 & NV28: NVIDIA Chips with AGP-8x Flavor
Need I go on? (The second article shows benchmarks at both 4X and 8X.)  
Take Care,
Richard