the most attractive change of version II lenses is weight loss IMO. perhaps reducing a 11.6lb lens to a 8.5 lb lens alone will be worth the price increase for those people who can hanhold their 500mm I(8.5lb). people sure expecting the weight of the new 600mm will be reduced to that level since it's weight of version I is as same as the 400mm I.


for those people(like me) who can't handhold the 8.5lb lens, then the 500mm II is more interesting if they can reduce it's weight to the 300mm 2.8 level which is 5.6lb, price is another fact that will put people to this lens even they can handle heavier weight.


Joel, if you get the 500 or 600 later and still want to keep the 300, will you consider to trade it for a 200mm 2.0/ I think I probably will if I were you.


another thing to watch is the IQ and AF of the version II lens TC III combo.since I have been thinking getting a longer one(500 or 600) too, if say the IQ and AF of 300mm II+2x TCIII combo is similar to 600mm I, for $7000, it's probably worth to upgrade to the 300mm II +TCs. sure I'll have 1 stop slower at 600mm, but I'll get better 300mm, and a handhodable 600mm don't forget a better IS.


according to Canon, in order to achieve the best performance that the new lenses and TCs can give, you need a 1D or 1Ds body. it's a lot harder for me to put $5000 on a body than to put $10000 on a lens though I'v been thinking about the 1D IV for long time. it's a damn expensive hobby anyways.


I can keep dreaming, but a 1dIV + 500mm II +TCsIII + trypod wimbly head combo sounds definitely too much for an amateur[]