Found the sweet spot on my memory last night - 475 FSB to give 1901Mhz at 7-7-7-18 1T 2.1v results in a 12125Mb/s read speed.

Core 1 (0-3) drops out running HyperPi now at this new frequency (4275) so looking to tune the GTLs later when I have more time.

Any feedback from 0701 bios ?. I'm still on 0501 and will prob stay with that in case any vdroop issues have been fixed on later bios's causing my voltages to be too high.