EF 400mm f/5.6L USM vs EF 300mm f/4.0L IS + TC1.4

On paper I prefer EF 300mm f/4.0L IS + TC1.4 due to:

1. Minimum focusing distance (telephoto macro). I would like to shot some insects.
2. IS. For handheld wildphoto, birds etc.....

If I am right for above TC1.4 II or TC1.4 III or 1.4 Kenko?

What's about sharpness at 400/420mm? At Photozone EF 400mm f/5.6L USM is very sharp, it seems EF 300mm f/4.0L IS with 1.4 could be the problem! The weight should be less than 1.5kg and the budget is roughly $1500. Any advice?

Thanks.