Neuro - is the last sentence missing a 'not' as in not using the the 70-200 now that you have the 100-300?
I am thinking that the kit just got reworked. 16-36 f4 w/ the adapter, 24-205 f2.8 and the 100-300 2.8 w/ a set of teleconverters (maybe only the 2x but need to see the IQ differential).
The 100-500 is a fantastic lens when there is some light and if you aren't needing subject separation or can do it on the computer.
Cons: on the 100-300... weight and filter size? I can use the filter kit on 82mm but the 100-300 gets huge!!!