Quote Originally Posted by Squidy View Post
... I've been told that's the only difference and the quality is similar to an L series lens in optical quality (but not build quality).
It's a true statement, much like it's also true that the moon is made of green cheese. Whoever told you that, I'd recommend doubting them if they said the sky is up or water is wet.

Get the 70-200mm f/4L, budget permitting. Cropping that to the 300mm framing will give much better results. If you actually need more native reach, consider the 70-300L (not the non-L, which is very soft >200mm).