Canon seems to keep coming out with new lenses, but you still can't buy the new 500 mm IS I or II or the 600, or. Seems silly to keep coming up with new lenses when they can't seem to provide the lenses that they already have "on the market" I have a 500 mm ver I and want to upgrade, but I am not even going to think about giving it up until production seems to be on the horizon. Anyone have any feedback or info?