Forgot to mention... When I spoke to MPC I'm told if I credit an I class bookable upgrade to another FF it will only credit to the original fare class. In my case that would be M economy class for an I class ticket. If this is the case bookable upgrades will not be much use to me. I'd prefer to fly another carrier in biz class and get the full quota of FF points for a cheaper fare than CX. I hope someone has had a different experience