Sure, the AGP hardly got saturated when doing most 3D stuff, but PCI express didn't replace AGP because it was too slow.
AGP got dropped because PCI express is so much easier (i.e. cheaper) to build into a motherboard (because you only need one interface). It also supported higher power profiles for attached cards and is way more versatile. Hence new PC's these days just have a bunch of PCI express slots, with PCI maybe included as a legacy slot (because most peoples old SoundBlasters etc. were PCI only).
The speed of AGP / PCI express is fairly redundant. The only large-scale transfers that go over the bus are when textures are loaded. After that, it's just DirectX/OpenGL communicating changes to the scene or new shader programs being loaded. The only impact the bus speed really has is making sure latency never becomes an issue.
AGP got dropped because PCI express is so much easier (i.e. cheaper) to build into a motherboard (because you only need one interface). It also supported higher power profiles for attached cards and is way more versatile. Hence new PC's these days just have a bunch of PCI express slots, with PCI maybe included as a legacy slot (because most peoples old SoundBlasters etc. were PCI only).
The speed of AGP / PCI express is fairly redundant. The only large-scale transfers that go over the bus are when textures are loaded. After that, it's just DirectX/OpenGL communicating changes to the scene or new shader programs being loaded. The only impact the bus speed really has is making sure latency never becomes an issue.