[NAME] Perhaps, the BIOS and Task Manager may be reporting what the RAM identifies itself as, that is, what is in the SPD (Serial Presence Detect) of the RAM modules or XMP (Extreme Memory Profile) although in the past Dell does not utilize the XMP. 
I recently purchased an 8950 with ddr5 ram advertised to run at 4400mhz. SiSoft Sandra, CPUID and HWiNFO all report the ram running at 2400mhz. These apps are all upgraded to handle ddr5 ram. The Dell bios reports 4400mhz, but the Dell bios is, well... made by Dell. What gives here? This is very expensive cutting edge ddr5 ram that looks like it is being throttled down. Has Dell misrepresented the ram speed?
XPS 8950, ram not as advertised?