Support for DDR3 2400(OC)/1866/1600/1333/1066 MHz memory modules
HyperX Savage 8GB (2 x 4GB) Memory Kit 2133MHz DDR3 CL11 DIMM - makers code is HX321C11SRK2/8
Reseating the CPU (with new paste) fixed the problem - it's now loading umpteen windows updates.
I'm still curious as to what running the board outside the case would have demonstrated, given it's an upgrade into a known working case.