Congrats on the new lens Dan
As most have said the Bigma is the no brainer and should be the 1st to go... however, I'd consider holding onto the 70-200 f/2.8 for a while, at least until you've lived with the 100-400 for a bit and are sure it give's you everything you need.
One thing I've noticed about the 100-400 (I own a copy aswell) is that it need's decent light to be at it's best, this is where the f/2.8 of the 70-200 would come in very handy... I'm not saying don't sell it, just don't be too hasty, you might need it depending on what you shoot.
