PCI Express is overrated. There hasn't been a PC yet that can flood 8x AGP, much less the theoretical max bandwidth of a PCI Express(PCIE?) card. The bottlenecks are as follows(in terms of performance increase): CPU --> Video bus speed, then Hard Drive transfer rate/bus speed, then CPU/memory transfer speed.
To take advantage of PCIE, two things need to occur:
1. Video cards need more memory and still faster processors
2. Hard Drives need to become faster to fill the pipe
Currently, with 8x AGP, it's a water hose feeding into a 6in drain pipe. There is no hope of filling that bandwidth.
BTW, OT
get this one The 5200 is much better than people give it credit for.