c300 is a great decision, i have one and it rocks! make sure to install RST 10 drivers, as they are better for 4k speeds than the stock msahci.sys, make sure you use Intel ports if you aren't already!

Yea i agree 16 gigs is a huge stress ont eh IMC, I am going to test 4 sticks at 1600 to see if its a 4 stick problem or 16 gigs problem. Also QPI upto 1.25 should be ok for benching.