RDRAM??

I recently inherited a computer that has 4 sticks of RDRAM for a total of 384 MB. 2x64MB, 2x128MB. The thing is that the 2 64MB sticks are 300MhZ and the 2 128MB sticks are 400Mhz. I was always under the impression that RDRAM was faster than SDRAM, but this computer seems to run slower than average. It has a 1.3 GhZ P4 processor. I’ve checked the all of the processes running and nothing seems out of the ordinary.

Is the mismatch in speed of the memory causing a problem? Also, is it possible to just replace the RDRAM sticks with DDR?

Thanks in advance.