So what would you recommend as the 'ultimate' test of memory reliability & stability? Linx? Prime95? HCI Memtest? Everyone seems to swear by Memtest86+ but you're the first person to suggest it's not overly reliable. Thanks for the rest of the advice, I really didn't expect this upgrade to be so tricky to get stable. But then, unreliability is usually related to overclocking and with Haswell over 1600MHz is 'overclocked' by default. So this is bringing back all the old tricks to make it stable without actual intentional overclocking. Can't deny I didn't expect it to be so tough to get a stock clocked system stable.