TC Upgrade - Worth it? II to III

Changing my motorsports kit up a bit and moving into a 300mm f/2.8. I am moving up from a 400 f/5.6 and shoot a crop body(pair of 7Ds). So my question is this. I already have a 1.4x and 2x EF II. Is it worth selling those off and going to the new III version? I will mostly be using the 1.4X if that makes any difference.

Thank you for the feedback. Not sure if there are any types of direct comparisons but read some reviews and cannot make up my mind.

There are many similar threads regarding this topic...

1.4II -> 1.4III - negligible difference.
2xII -> 2xIII - significant improvement in terms of AF speed, colour/contrast and sharpness, esp when used with tele primes like you have.

Here's a comparison of the 300mm (version 1) with the 1.4x II and III. Not taken with the 7d, but should give you an idea. For some reason, they don't have shots of the 300 version II with the 1.4x II.