I don't think EK releases any official results, but the numer is very, very high. I think this is partly because Silver/Golds don't get much advantage in terms of upgrades compared to non members and Blues (no SWUs, EVIPs, same mileage availability and redemptions etc) so maybe EK tries to compensate by going crazy with opups. Or it could just be that EK yield management sucks
FWIW my grandfather, as a Gold, has been op upped (J-->F) on 25% of all his flights, mostly DXB-BKK,DXB-KHI,DXB-LHR,DXB-ZRH and vv.
Cheers