XFS is fast file system, but it can be tweaked to be a little bit faster. There are a tweak I am using with my disks:
You can create xfs filesystem with a 128 megabyte log and 8 allocation groups.
# mkfs.xfs -f -l internal,size=128m -d agcount=8 /dev/md0
After that you can mount filesystem with 8 log buffers, and atime and diratime disabled.
# mount -t xfs /dev/md0 /mnt/gentoo -o noatime,nodiratime,nobarrier,logbufs=8
Also do NOT forget to align your partitions.