I did not have flickering or blackouts on my iMac and had decided against applying the firmware update. This morning I was feeling brave and did the update. First thing I noticed was the increased speed in the Aperture loupe. Before the update, using the loupe when zoomed in at 100 % , it's movement was jerky and a bit sticky at times. I was told by somebody on another forum that it was because the iMac video cards can't handle Aperture. I could live with this, as it was usable and much better than my old iMac. But the firmware update has made it perfect, I am now EXTREMELY happy with my iMac. 
Just need to get the screen replaced to solve the yellow gradient on the bottom of the screen.
Just need to get the screen replaced to solve the yellow gradient on the bottom of the screen.