I have exactly the same as you.
70-200 f4 IS
I just brought the 70-200 a few days ago and its nice. I spent a day with it on my 5d3 with canon strap and it was fine, not too heavy.
If you need more reach, you could consider the kenko 1.4x extender, but it will stop it down to f5.6 though, autofocus is fine, at least to my beginner level.
Also your question about the 24-70 mkII, you already have that focus range from the 24-105, so would buying the 70-200 benefit you more now? or at least the period from now till the release of the 24-70 mk II
I know the new upcoming mkII is a completely different lens and you cant compare it to the 24-105, it should have better components, f2.8, better everything, but its release date has been delay.