We first noticed a dip in QD2 sequential read performance on the 1.2TB SSD 750 just prior to publishing our review. We ran an additional test to verify our initial results. Unfortunately, the 400GB model encounters the same hit, and performance drops off lower than sequential reads at QD1 and QD4.
Samsung's SM951 512GB delivers higher sequential read performance at lower queue depths, but can't match the same peak numbers as Intel's SSD 750 at high queue depths.
It's important to understand that most client workloads happen at low queue depths. Drive vendors typically don't specify performance at those queue depths, where it really counts. And we don't blame them. Peaks always looks better on paper. They just don't always represent usable performance.