Thanks for the comments Aidan. Yes I also think the second shot is the best. I was trying out the 2x on the 600 with 1D MKIII just to see if there was any serious image degradation. I took a few shots at f8, ISO 800 and the DOF looked too shallow. I closed the lens to f11 and in general the results were better. I might try later on to push the ISO up a bit more.
On the whole I am quite impressed with the performance of the 2x converter.
That’s some combination of gear, I had a Canon 70-300mm IS USM close up on a Dragon Fly but I had to be fairly close at the 300mm end to get it really full in the frame.
How much would a 600 prime set you back in this weather?