Answering my own problem (told ya I would do it, see my comments)
(I've rewritten the question title as I have found a solution which works for me the same)
I bought another USB3 ExpressCard 34 (see below) and this card has the Fresco FL1100 chipset which is supported natively by MacOS X (see below).
Plugged it in, then plugged in the drives and they were all recognised, even those on a USB3 hub by Pluggable.
Quick benchmarks:
Copy a single 47Gb file from an external USB3 HD to the Mac's SSD.
Transcend USB3 7200rpm external 2Tb Drive (rugged model) copy to Mac's own SSD on USB2 (two): Estimated copy time: about 27 minutes.
Transcend USB3 7200rpm external 2Tb Drive (rugged model) copy to Mac's own SSD on USB3 (three) port on the ExpressCard 34 USB3 card: Estimated copy time: about 9 minutes.
Conclusion: copying is approx 3 times faster with USB3 than USB2 in this real life (but not scientific) test.
Other copy tests indicated at least 2 times faster (with many files to copy, so I'd expect the overhead of multiple files reduces the performance).
Where to buy a ExpressCard 34 with the FL1100 chipset:
and on ebay
References about MacOS X natively supporting 3rd-party chipsets such as the Fresco FL1100:
I'd still hold onto my Renesas card in case 3rd-party support becomes available later.
Update
This solution also works perfectly fine with OS X El Capitan, and Windows 10 64bit Pro via Bootcamp.
Update 2
This solution also works perfectly fine with the latest version of OS X Sierra - because I have this running on my mid 2010 Mac Book Pro 17", with the ExpressCard inserted into it.
I think the ongoing support is because some Macs with built in USB3 used the FL1100 chipset and therefore those Macs that are on the supported list for Sierra that have this chipset will work. Therefore Macs which can have after-market/3rd-party FL1100-based USB3 cards added to them via ExpressCard (notebooks) and PCI (Express) card (desktop - Mac Pro) will also be supported by the OS.
However, keep monitoring the situation for future versions of Mac OS X, in case the list of supported Macs changes if they drop those Macs with FL1100 support and therefore leave out the driver for it in future versions of the OS to focus maintenance costs on hardware that they choose to support.