Is there a compatability issue?

[Briton]

Hi. A friend of mine has just bought a PC using a E6600 C2 and got 2 Gig of PC2-5300 RAM. He has been told that was a waste of money as the RAM could actually run slower than PC2-4200. Is that true?

 

[Briton]

I doubt he will actually as he's not very confident messing with settings.