When it came to comparing anything to the Geforce 6200, you have to be more specific. The original PCIe 6200 actually had the 6600 core silicon, with some pipelines disabled. It was pretty good, but overpriced for the time, and didn't sell well. The AGP version included a defect in the pixel shaders that required running any game with a lot of shader code in a window, not full screen, but it was a 128 Bit memory card, same as the PCIe card was (and same as the X300 is).
The 6200A replaced both the AGP and the PCIe GPUs, and is 64 Bit, so half as good. It was based on the defective silicon, and that defect persisted into the 7100, 7200, 7400, and the 7300 GS that followed it.
So, an X300 was overshadowed by the oldest, original pair of 6200s, but in turn was far better than the 6200A (and of course there was an X300 SE, which as you can guess, had its memory system cut from 128 Bits to 64 Bits).