On a MacBookPro Retina late 2013er connected directly to the USB3 port and HFS + - then measured with AJA write speed (I was just curious): Writing about 125 MB / s, read about 155 MB / s - very good values, the rule of are kept constant.
In practice, this will vary - but the copying of the internal via PCIe SSD connected the values are in the fast area: Mixed files (Small & Medium) went copying con ca 25GB quite fast within about 4 minutes.
Gladly again (could the stick as Amazon Flash offer even buy something cheaper)