Well how happy am I ?
Re-inserted XFI, no problems, couple of boots, still fine. Checked I still had latest driver, I did, installed, several warm and cold boots later all is still well.
Put the USB3 driver back on, still fine!
DM if you are ever in Sheffield, I owe you a large bottle of your favourite; I've been on this 4 frustrating weeks and was losing the will to live. Now I can finally do what I bought the damned thing for - play games faster!
Such a simple solution - you are a godsend. Enough gushing, but thank you very much indeed!