There’s been some updates to the AHCI driver.  Matthew Dillon outlined the changes, with the biggest one being support for FIS Based Switching.  FBS is the ability to send simultaneous streams of data to and from multiple drives on a port multiplier.  Support for it is rare and quirky, but it should significantly improve throughput on a compatible port multipler.  Read his writeup for details, including on how to back up your kernel.