PCI Graphic Card - OK For Aero ?

I would like buying a graphic card with a H.264 hardware support for my Pentium 4.

This card will be useful for the next version of Adobe Flash Player (10.1) too.

Unfortunately, my motherboard doesn't have a PCI-E slot : only AGP 4x and PCI 2.2.

It can boot with a PCI card as primary VGA and it also supports PCI 2.1 card.

As Flash 10.1 is more optimized for Nvidia products and the ATI support of their

AGP HD cards is very bad in Windows 7, Vista and even XP (there is no WHQL driver),

I prefer buying a DirectX 10 card from Nvidia. But there is no AGP DirectX 10 Nvidia.

So, I has to choose a PCI (not PCI-E) graphic card.

My current graphic card is a Gigabyte GeForce 6200 AGP 8x.

Windows Aero runs but, for example, "Flip 3D" is pretty slow with a lot of windows.

My next graphic will probably be a EVGA/Sparkle GeForce 9400GT or Albatron 8600GT.

Note : what is the best manufacturer ==> EVGA, Sparkle or Albatron ?

But I wonder about Windows Aero : Isn't a PCI bus too slow for Windows Aero ?

Compared to my GeForce 6200 AGP 8x (running at 4x due to my motherboard),

will 3D Windows GUI (called Aero) be faster or slower with a GeForce 9400GT PCI ?

What about GeForce 8600GT PCI ? I worry because PCI bus is slower than AGP bus.

In short, will there be performance issues with Windows Aero ? Or not ?

Could I sell my GeForce 6200 instead of leaving on my computing (with a PCI card) ?