Well I'm confused.
Ran 6 passes of memtest on both sticks individually, no errors. Ran it again with both sticks in, no errors.. When previously I had errors on the 2nd pass.
Tried LinPack and results of it indicate it's stable so far (wow this app actually slows down my pc, just opening a browser is slow)
Running size of 21000 for "Maximum memory requested that can be used = 3528424096", which brings my free ram down to about 152MB when it's running, and in the past 30mins all Residuals have matched.