I have a portable HDD on USB 3.0, and soon I'll have a 32gb flash drive on USB 3.0 as well.
My motherboard is pretty old - and the next time I'll upgrade it is when I get a new CPU/mobo/ram.
Slots on my mobo:
PCIE X16 - For my GTX 260
I'm considering purchasing a PCI express X1 card like this - http://www.ebay.com.au/itm/PC-Laptop-2-USB3-0-Ports-PCI-E-PCI-Express-X1-Card-New-/280772000446?pt=AU_Networking&hash=item415f50babe
Now the question:
What are realistic (read/write) speeds I'll get in this setup, assuming I have 1 USB 3 device connected at a time, and the bottleneck is the PCIE?