D820 RAM speed support

It looks like your ram is deffinately mismatched, and even though I don't have a d820, from the dell specs it says you can run dual channel 667, so not only are you probably losing bandwidth since both are probably running 533 (max of the kingston stick), but since they're not the same your losing the dual channel bandwidth.  Return them for a dual channel kit or get your money back.  The speeds you showed are the options you can run with each stick, if you look under the memory tab in cpuid you'll find what they are currently running at.  When you shop for sticks look for the ones with the lowest timings, especially the cas latency (1st number).  DDR2 usually has crappier timings than regular DDR due to its nature and partially due to the fact Intel chips don't have integrated mem controllers, so aim for DDR2 667 (333 doubled).  Hope this helps