So much misinformation here!
I can't imagine a meaningful benchmark between SAS and SATA and I wouldn't bother looking for one. This is like benchmarking a six passenger minivan versus high-speed bullet train.
1) At any given point in time, the SAS interface is always twice as fast as SATA -- and 4x faster if you consider that SAS is dual-ported and full duplex. Today, SAS is 12gbits, dual-ported and full duplex while SATA is 6gbits, single-ported and single duplex. There has never been a time when SAS and SATA were both 6gbits.
2) The main reason for using a SAS vs SATA drive is when many disks or ssd devices are sharing a SAS domain. Now as many here already know, your AVAGO (LSI) or equivalent RAID adapter can talk to either SAS or SATA devices via 8x12gbit SAS ports. For the most demanding workloads, I have seen comparative testing in our labs showing a "fully loaded" 12gbit SAS RAID adapter connected via SAS expanders with 16x SAS SSDs and this is up to 8x faster than the exact same adapter with 16x SATA SSDs, and in this case we are not even leveraging the dual-ports on the SAS drives!
3) There are numerous features built into SAS drives that (in the presence of lots of bus activity) help them reduce contention and allow these drives to get on and off the bus much, MUCH faster than a SATA drive can on the same SAS bus with the same workload.
Bottom line is SAS vs. SATA is all about the use-case. The comparison of a single SATA drive vs a single SAS drive is a meaningless exercise.