I just backed-up my entire system to my FAP drive using the free drive imaging program DriveImage XML. Here is how long it took:
C: drive (OS) - 10.7GB
11 min = 0.97 GB/min = 16.6MB/sec
D: drive (data) - 31.0GB
48 min = 0.65 GB/min = 11.0MB/sec
My FAP drive is almost full, so the data will have been stored on the slowest inner-part of the drive, so these are probably worst-case figures.
I highly recommend DriveImage XML to backup your entire system.