Combining together the performance meter and the inline version of the USB write routines (i.e. with quite some optimization active), I got pretty decent throughput results: circa 16.42 kB/s!
The real highest throughput value is slightly higher than this as a genuine save operation would not have the overhead of the meter running in parallel, but you get the idea 🙂
To give an idea of how fast this is: assuming the same speed for read operations (read and write speeds are similar with read slightly faster) USBhost-64 would be fast enough to load a full-screen colour hires animation at 1 fps, or full-screen constant colour+video RAM hires animation at 2 fps.
Non full-screen animations would take less time to load so one could achieve better fps values.
Example applications would be: slideshows, presentations, subtitles, etc.