IS on long lenses question

I know there are different generations of IS, and I know that some work on tripods and some don't. Not part of my question. It seems that one might assume that when they make a 300 (for example,) they make the IS to handle expected vibrations/shake. And, when they make a 600 they do the same. So, when you put a 2X TC on a 300 IS lens, even though you still have IS (great feature,) it is not going to work as well at 600 as the IS on the 600 would. Yes, no?

I would say no, just beacuase the 600 IS is meant for 600mm focal length. the 300 is not, It will still work I just dont think quite as good.

I'll let someone who knows more tell you, dont listen to me i could be wrong.

i would think it would work just the same. but puting a converter on slow,s down focusing by around 40% so this set up wont be as fast as a 600mm.
Rob.

It'll work just the same, but you have to remember that "minimum handholdable speed (whatever that may be for you)" doubles when you put that 2x TC on the lens and you lose 2 stops of aperture, so the 2-3 stop gain starts 3 stops further up. Net result - put a 2x TC on a lens and engage IS to be able to hold it where you would without either the TC or IS.