I'm a fan of both PostgreSQL and SQL Server, but I think these numbers are very workload-specific. I've gotten 1GB/s throughput on SQL Server 2012 on spinning disks and CPUs older than the E5620, so I've no doubt that same workload would exceed 2GB/s on your hardware. The apples-to-apples comparison here is between the two versions of PG where the performance improvement is clear. It's harder to do an apples-to-apples comparison between PG and SQL Server because the optimal schema and queries for a particular workload are likely to differ for each of them.