Overlapping focal ranges

So here's my dilemma, as you can see in my sig, I have both the 70-200 f/2.8L IS and also the 100-400 f/4.5-5.6L IS.

My 100-400 hasn't really seen any use since I got the 70-200 (but then again I haven't done much surfing or jetski shoots since then either)

My question is, think I could dump the 100-400 and get away with a TC 2x III and my 70-200 ?

What would I really lose here ?

I hate to have $$ tied up and I could use the $$ towards another body, which by the way will be a 1dmk3.

Thoughts ?

My suggestion would be to rent a 2x III and give it a go, comparing the two. Then you can judge for yourself whether the 70-200 + 2x is sufficient for those times you need more magnification. If it is, then you know you can let the bigger lens go. I have both the 70-200/4 and 100-400 and find I don't use the 70-200 so much, but it's still a useful sharp lens and I chose to keep it.

My 100-400 only comes out when I'm doing sports or wildlife, generally speaking. The 70-200 is my go-to telephoto. Both definitely have their place.

I got a cheaper sigma for my super telephoto needs (rare occurrence).