pfsense 2.4.0-RELEASE (amd64) does support UASP.
#camcontrol devlist
<st1000nm 0011="" pt0d="">at scbus0 target 0 lun 0 (pass0,da0)
#camcontrol inquiry da0
pass0: <st1000nm 0011="" pt0d="">Fixed Direct Access SPC-4 SCSI device
pass0: Serial Number 000000123BA3
pass0: 400.000MB/s transfers
#usbconfig
ugen0.1: <0x8086 XHCI root HUB> at usbus0, cfg=0 md=HOST spd=SUPER (5.0Gbps) pwr=SAVE (0mA)
ugen0.2: <vendor 0x05e3="" usb2.0="" hub="">at usbus0, cfg=0 md=HOST spd=HIGH (480Mbps) pwr=SAVE (100mA)
ugen0.3: <vendor 0x04d9="" usb="" keyboard="">at usbus0, cfg=0 md=HOST spd=LOW (1.5Mbps) pwr=ON (100mA)
ugen0.4: <vli manufacture="" string="" vli="" product="">at usbus0, cfg=0 md=HOST spd=SUPER (5.0Gbps) pwr=ON (2mA)</vli></vendor></vendor></st1000nm></st1000nm>
This is with this USB to SATA device and this HDD.
My next mission is to figure out how to test the actual speed it achieves.
Edit: build in speed test:
#diskinfo -tv /dev/da0p2
/dev/da0p2
512 # sectorsize
996431888384 # mediasize in bytes (928G)
1946156032 # mediasize in sectors
0 # stripesize
544768 # stripeoffset
121142 # Cylinders according to firmware.
255 # Heads according to firmware.
63 # Sectors according to firmware.
000000123BA3 # Disk ident.
Seek times:
Full stroke: 250 iter in 5.089351 sec = 20.357 msec
Half stroke: 250 iter in 3.598658 sec = 14.395 msec
Quarter stroke: 500 iter in 5.795468 sec = 11.591 msec
Short forward: 400 iter in 1.517583 sec = 3.794 msec
Short backward: 400 iter in 2.655790 sec = 6.639 msec
Seq outer: 2048 iter in 1.572585 sec = 0.768 msec
Seq inner: 2048 iter in 1.577754 sec = 0.770 msec
Transfer rates:
outside: 102400 kbytes in 0.831469 sec = 123156 kbytes/sec
middle: 102400 kbytes in 0.863127 sec = 118638 kbytes/sec
inside: 102400 kbytes in 1.456835 sec = 70289 kbytes/sec