This hasn't been tested, but after asking around on BG I got one of the math guys to give me a possible cure CE mod based on the rate of decline from ~75.

For curing a level 90 target, 40/64, or 0.625. Compared to level 75's 0.727 modifier.

We will, of course, want to get this tested once the servers are back up. But for the moment it seems like a reasonable number to use.