Hey I am looking at buying something in that range.

I am on a really tight budget although I have a 75-300 III lens and I would like to buy something a bit better, especially on the long end.

What do you think of the old 100-300 5.6 L lens? (I can't really find it anywhere for sale though)

Or are there any other lenses from different manufacturer worth considering?

Thank you.

Mirc.