Congratulations! I got mine 2 weeks ago!
I suggest to use it as much as possible to see if you are comfortable with your camera/lens combination...
I personally find it big and heavy so I am keeping my 70-200 f/4L IS too (although there is an overlap here)
I think I will use the f 2.8 version mostly for portraits, action and low light ... assuming I will not have to
walk for a long time with a lot of gear. In that case it is the f/4 version (which will allow me to bring with me one more lens for the same total weight and space in the bag...)
Enjoy your lens...
