Dell would not sell you that computer if it didn't work.  3400HM is a special configuration of ram in certain slots. Check the manual  Pg 46.  
I ordered an R10 with the 64GB XMP 3400MHz  memory configuration.  I've now been reading that the R10 only supports up to 64GB XMP 3200MHz?  Why would they offer the 3400MHz config if this memory not supported at that speed?  Did I make a mistake?
Aurora R10, 64GB XMP 3400MHz system memory configuration?